Fix crash when sorting out_of_range columns

Fix crash while sorting the right part of equal sign with column-selection:

100/20 = 5

1/3    = 0.333

22/7   = 3.14285714286

Note that empty lines between the numbers are intentional.

Fix #5865, fix #3391, close #3771

PowerEditor/src/MISC/Common/Sorters.h

@@ -48,6 +48,12 @@ protected:
 	{
 		if (isSortingSpecificColumns())
 		{
+			// prevent an std::out_of_range exception
+			if (input.length() < _fromColumn)
+			{
+				return TEXT("");
+			}
+
 			return input.substr(_fromColumn, 1 + _toColumn - _fromColumn);
 		}
 		else