vcl: don't assert when lack of unit is intentional

The Writer zoom dialog had this issue. Also change the drawinglayer
gradient background tabpage to stop using a custom unit text, when the
real unit text will be set from code anyway.

Change-Id: Ib2e12572abb5c407b7c49dfa4a34dbdd6b6068d4

cui/uiconfig/ui/gradientpage.ui

@@ -153,7 +153,7 @@
                       </packing>
                     </child>
                     <child>
-                      <object class="GtkSpinButton" id="anglemtr: degrees">
+                      <object class="GtkSpinButton" id="anglemtr:0">
                         <property name="visible">True</property>
                         <property name="can_focus">True</property>
                         <property name="invisible_char">●</property>

vcl/source/window/builder.cxx

@@ -684,7 +684,9 @@ namespace
         else if (sUnit == "%")
             eUnit = FUNIT_PERCENT;
 
-        assert(eUnit != FUNIT_NONE); //unknown unit
+        // if lack of unit is not intentional
+        if (sUnit != "0")
+            assert(eUnit != FUNIT_NONE); //unknown unit
 
         return eUnit;
     }