QString perf improvement : removal of useless test

Removed a test in QStringAlgorithms trimmed_helper. That test is not
needed because both null / empty QStrings are already handled by the
previous test, other cases are handled just fine by the general case.

Change-Id: I26db1142a656a7d06dfdd6b3b8f8a3ee6ca22302
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qstringalgorithms_p.h

@@ -101,8 +101,6 @@ template <typename StringType> struct QStringAlgorithms
 
         if (begin == str.cbegin() && end == str.cend())
             return str;
-        if (begin == end)
-            return StringType();
         if (!isConst && str.isDetached())
             return trimmed_helper_inplace(str, begin, end);
         return StringType(begin, end - begin);