Pass custom config file path as absolute

Author: Mieszko Boczkowski

platforms/js/build_js.py

@@ -246,7 +246,7 @@ def build_loader(self):
 
     log.debug("Args: %s", args)
 
-    os.environ["OPENCV_JS_WHITELIST"] = args.config
+    os.environ["OPENCV_JS_WHITELIST"] = os.path.abspath(args.config)
 
     if 'EMMAKEN_JUST_CONFIGURE' in os.environ:
         del os.environ['EMMAKEN_JUST_CONFIGURE']  # avoid linker errors with NODERAWFS message then using 'emcmake' launcher