Utils: Properly terminate loop in Environment::diff()

The iterator needs to be tested against the end() of
the same container.

Change-Id: Ia4d208650d922d529ea074d4cd0eac9f4ac76b87
Reviewed-by: BogDan Vatra <bogdan@kde.org>
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>

src/libs/utils/environment.cpp

@@ -376,7 +376,7 @@ QList<EnvironmentItem> Environment::diff(const Environment &other) const
         if (thisIt == constEnd()) {
             result.append(EnvironmentItem(otherIt.key(), otherIt.value()));
             ++otherIt;
-        } else if (otherIt == constEnd()) {
+        } else if (otherIt == other.constEnd()) {
             EnvironmentItem item(thisIt.key(), QString());
             item.unset = true;
             result.append(item);