qdir: Fix a condition typo

A part of conditional expression is always false: if "c > 'z'"

Task-number: QTBUG-71156
Change-Id: I6ee20c45d80e476d97e59167c481b157e4a233d0
Reviewed-by: Mikhail Svetkin <mikhail.svetkin@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qdir.cpp

@@ -74,7 +74,7 @@ static QString driveSpec(const QString &path)
     if (path.size() < 2)
         return QString();
     char c = path.at(0).toLatin1();
-    if (c < 'a' && c > 'z' && c < 'A' && c > 'Z')
+    if ((c < 'a' || c > 'z') && (c < 'A' || c > 'Z'))
         return QString();
     if (path.at(1).toLatin1() != ':')
         return QString();