opencl SERIESSUM does not handle plain double arguments

sc_subsequent_filters_test in ScFiltersTest::testFunctionsODS() also
checks "SERIESSUM(2;3;2;3)", which the opencl code does not handle.
At least bail out gracefully instead of returning 0.

Change-Id: I154dca8cc437a6225b4eb98012232d80683f0114
Reviewed-on: https://gerrit.libreoffice.org/64242
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

sc/source/core/opencl/op_math.cxx

@@ -3081,7 +3081,7 @@ void OpQuotient::GenSlidingWindowFunction(std::stringstream &ss,
 void OpSeriesSum::GenSlidingWindowFunction(std::stringstream &ss,
     const std::string &sSymName, SubArguments &vSubArguments)
 {
-    if( vSubArguments.size() != 4){return;}
+    CHECK_PARAMETER_COUNT(4,4);
     ss << "\ndouble " << sSymName;
     ss << "_"<< BinFuncName() <<"(";
     for (size_t i = 0; i < vSubArguments.size(); i++)
@@ -3185,6 +3185,8 @@ void OpSeriesSum::GenSlidingWindowFunction(std::stringstream &ss,
             ss << "))\n";
             ss << "        return 0;\n";
         }
+        else
+            throw Unhandled(__FILE__, __LINE__);
     }
     ss << "    return res;\n";
     ss << "}";