QString: Avoid searching for a needle which is longer than the hay

Avoid incurring the cost of converting the latin1 data in that case.

Several existing QString unit tests excercise the new code path.

Task-number: QTBUG-52617
Change-Id: I27256d9e7db34f09543e244a79d754ff7932f0d0
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qstring.cpp

@@ -10005,6 +10005,9 @@ static inline int qt_find_latin1_string(const QChar *haystack, int size,
                                         QLatin1String needle,
                                         int from, Qt::CaseSensitivity cs)
 {
+    if (size < needle.size())
+        return -1;
+
     const char *latin1 = needle.latin1();
     int len = needle.size();
     QVarLengthArray<ushort> s(len);