ProcessStub: Handle failed ftell

Change-Id: I07967ee4f05daa43262d205e2113325b96b429f6
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/libs/utils/process_stub_unix.c

@@ -223,6 +223,10 @@ int main(int argc, char *argv[])
         }
         fseek(envFd, 0, SEEK_END);
         size = ftell(envFd);
+        if (size < 0) {
+            perror("Failed to get size of env file");
+            doExit(1);
+        }
         rewind(envFd);
         envdata = malloc(size);
         if (fread(envdata, 1, size, envFd) != (size_t)size) {