qmake: fix assertion on Windows when DESTDIR is empty in static libs

Basically replacing project->values("foo").first() with
project->first("foo") which does a null check.

Task-number: QTBUG-12851
Reviewed-by: ossi

1 files changed, 6 insertions, 3 deletions

diff --git a/qmake/generators/win32/winmakefile.cpp b/qmake/generators/win32/winmakefile.cpp
index c36cc9c..4944d06 100644
--- a/qmake/generators/win32/winmakefile.cpp
+++ b/qmake/generators/win32/winmakefile.cpp
@@ -472,10 +472,13 @@ void Win32MakefileGenerator::processRcFileVar()
         resFile.replace(".rc", Option::res_ext);
         project->values("RES_FILE").prepend(fileInfo(resFile).fileName());
         if (!project->values("OBJECTS_DIR").isEmpty()) {
-            if(project->isActiveConfig("staticlib"))
-                project->values("RES_FILE").first().prepend(fileInfo(project->values("DESTDIR").first()).absoluteFilePath() + Option::dir_sep);
+            QString resDestDir;
+            if (project->isActiveConfig("staticlib"))
+                resDestDir = fileInfo(project->first("DESTDIR")).absoluteFilePath();
             else
-              project->values("RES_FILE").first().prepend(project->values("OBJECTS_DIR").first() + Option::dir_sep);
+                resDestDir = project->first("OBJECTS_DIR");
+            resDestDir.append(Option::dir_sep);
+            project->values("RES_FILE").first().prepend(resDestDir);
         }
         project->values("RES_FILE").first() = Option::fixPathToTargetOS(project->values("RES_FILE").first(), false, false);
 	project->values("POST_TARGETDEPS") += project->values("RES_FILE");