fdo#49421: do not divide by zero when scrollbar cannot be moved

Change-Id: I63338f6c2cfa3d206260b536a44de3d51fcd5710

vcl/source/control/scrbar.cxx

@@ -63,6 +63,8 @@ using ::rtl::OUString;
 
 static long ImplMulDiv( long nNumber, long nNumerator, long nDenominator )
 {
+    if (!nDenominator)
+        return 0;
     double n = ((double)nNumber * (double)nNumerator) / (double)nDenominator;
     return (long)n;
 }