always check for baseEnv init failure

sync up; this doesn't actually do anything in qmake.

creator's file watcher can trigger many parallel, entirely
non-hierarchical project reloads. if there is enough of them to exceed
the thread pool size, some will be serialized already by qtconcurrent,
not by our wait condition. these should notice a faulty spec, too.

Change-Id: I8ce40cb90fbc28045127881d57ec94e125df79af
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
(cherry picked from qtcreator/759d0a69dd3973b4785b6f9412f46666a05cdf85)

qmake/library/qmakeevaluator.cpp

@@ -1355,6 +1355,8 @@ QMakeEvaluator::VisitReturn QMakeEvaluator::visitProFile(
                     return ReturnFalse;
             }
 #ifdef PROEVALUATOR_THREAD_SAFE
+            else if (!baseEnv->isOk)
+                return ReturnFalse;
         }
 #endif