QDoc: Remove fatal exit when not finding an index directory.

QDoc would exit with exit code 1 when an index directory is not found,
this behaviour was probably a bit too strict.

Change-Id: If62fe1aeac4392002fa7419f6abcb62ed41c2beb
Reviewed-by: Martin Smith <martin.smith@nokia.com>

src/tools/qdoc/main.cpp

@@ -503,7 +503,6 @@ int main(int argc, char **argv)
             }
             else {
                 qDebug() << "Cannot find index directory" << argv[i];
-                return EXIT_FAILURE;
             }
             i++;
         }