corrected initialization of output_folder in facereco examples

modules/contrib/doc/facerec/src/facerec_eigenfaces.cpp

@@ -70,7 +70,7 @@ int main(int argc, const char *argv[]) {
         cout << "usage: " << argv[0] << " <csv.ext> <output_folder> " << endl;
         exit(1);
     }
-    string output_folder;
+    string output_folder = ".";
     if (argc == 3) {
         output_folder = string(argv[2]);
     }

modules/contrib/doc/facerec/src/facerec_fisherfaces.cpp

@@ -70,7 +70,7 @@ int main(int argc, const char *argv[]) {
         cout << "usage: " << argv[0] << " <csv.ext> <output_folder> " << endl;
         exit(1);
     }
-    string output_folder;
+    string output_folder = ".";
     if (argc == 3) {
         output_folder = string(argv[2]);
     }

modules/contrib/doc/facerec/src/facerec_save_load.cpp

@@ -70,7 +70,7 @@ int main(int argc, const char *argv[]) {
         cout << "usage: " << argv[0] << " <csv.ext> <output_folder> " << endl;
         exit(1);
     }
-    string output_folder;
+    string output_folder = ".";
     if (argc == 3) {
         output_folder = string(argv[2]);
     }