Fix warning about non-void function not returning anything

Found by ICC 17 Beta on Windows.

Change-Id: Ib57b52598e2f452985e9fffd1458b6990b70837a
Reviewed-by: Robin Burchell <robin.burchell@viroteck.net>

src/corelib/kernel/qcoreapplication.cpp

@@ -2144,7 +2144,6 @@ QString QCoreApplication::applicationFilePath()
             QCoreApplicationPrivate::setApplicationFilePath(fi.canonicalFilePath());
             return *QCoreApplicationPrivate::cachedApplicationFilePath;
         }
-        return QString();
     }
 #endif
 #if defined( Q_OS_UNIX )
@@ -2190,9 +2189,8 @@ QString QCoreApplication::applicationFilePath()
         }
     }
 
-    return QString();
 #endif
-    Q_UNREACHABLE();
+    return QString();
 }
 
 /*!