sc: Let SKEW/SKEWP raise #!DIV/0 when < 3 numbers are given

as ODF 1.2 mentions such constaints of these functions, and
Excel's documentation also admits it with more specific remark:
<https://support.office.com/en-us/article/skew-function-bdf49d86-b1ef-4804-a046-28eaea69c9fa>
<https://support.office.com/en-us/article/skew-p-function-76530a5c-99b9-48a1-8392-26632d542fcb>

Change-Id: If19350997ddcb6f0fb36e29e090e260c3ae3d262
Reviewed-on: https://gerrit.libreoffice.org/61130
Tested-by: Jenkins
Reviewed-by: Eike Rathke <erack@redhat.com>

sc/qa/unit/data/functions/statistical/fods/skew.fods

@@ -5047,10 +5047,18 @@
      <table:table-cell table:number-columns-repeated="2"/>
     </table:table-row>
     <table:table-row table:style-name="ro6">
-     <table:table-cell table:style-name="ce27"/>
-     <table:table-cell/>
-     <table:table-cell table:style-name="ce28"/>
-     <table:table-cell table:style-name="ce32"/>
+     <table:table-cell table:style-name="ce27" table:formula="of:=SKEW(1;2)" office:value-type="string" office:string-value="" calcext:value-type="error">
+      <text:p>#DIV/0!</text:p>
+     </table:table-cell>
+     <table:table-cell table:formula="of:#DIV/0!" office:value-type="string" office:string-value="" calcext:value-type="error">
+      <text:p>#DIV/0!</text:p>
+     </table:table-cell>
+     <table:table-cell table:style-name="ce28" table:formula="of:=ERROR.TYPE([.A32])=2" office:value-type="boolean" office:boolean-value="true" calcext:value-type="boolean">
+      <text:p>TRUE</text:p>
+     </table:table-cell>
+     <table:table-cell table:style-name="ce32" table:formula="of:=FORMULA([.A32])" office:value-type="string" office:string-value="=SKEW(1,2)" calcext:value-type="string">
+      <text:p>=SKEW(1,2)</text:p>
+     </table:table-cell>
      <table:table-cell table:number-columns-repeated="4"/>
      <table:table-cell office:value-type="float" office:value="900000031" calcext:value-type="float">
       <text:p>900000031</text:p>

sc/qa/unit/data/functions/statistical/fods/skewp.fods

@@ -5041,10 +5041,18 @@
      <table:table-cell table:number-columns-repeated="2"/>
     </table:table-row>
     <table:table-row table:style-name="ro6">
-     <table:table-cell table:style-name="ce27"/>
-     <table:table-cell/>
-     <table:table-cell table:style-name="ce28"/>
-     <table:table-cell table:style-name="ce32"/>
+     <table:table-cell table:style-name="ce27" table:formula="of:=SKEWP(1;2)" office:value-type="string" office:string-value="" calcext:value-type="error">
+      <text:p>#DIV/0!</text:p>
+     </table:table-cell>
+     <table:table-cell table:formula="of:#DIV/0!" office:value-type="string" office:string-value="" calcext:value-type="error">
+      <text:p>#DIV/0!</text:p>
+     </table:table-cell>
+     <table:table-cell table:style-name="ce28" table:formula="of:=ERROR.TYPE([.A32])=2" office:value-type="boolean" office:boolean-value="true" calcext:value-type="boolean">
+      <text:p>TRUE</text:p>
+     </table:table-cell>
+     <table:table-cell table:style-name="ce32" table:formula="of:=FORMULA([.A32])" office:value-type="string" office:string-value="=SKEWP(1,2)" calcext:value-type="string">
+      <text:p>=SKEWP(1,2)</text:p>
+     </table:table-cell>
      <table:table-cell table:number-columns-repeated="4"/>
      <table:table-cell office:value-type="float" office:value="900000031" calcext:value-type="float">
       <text:p>900000031</text:p>

sc/source/core/tool/interpr3.cxx

@@ -3323,6 +3323,13 @@ void ScInterpreter::CalculateSkewOrSkewp( bool bSkewp )
     std::vector<double> values;
     if (!CalculateSkew( fSum, fCount, vSum, values))
         return;
+     // SKEW/SKEWP's constraints: they require at least three numbers
+    if (fCount < 3.0)
+    {
+        // for interoperability with Excel
+        PushError(FormulaError::DivisionByZero);
+        return;
+    }
 
     double fMean = fSum / fCount;