Always extract extensions from the original error if possible

Author: leebyron

src/error/GraphQLError.js

@@ -175,7 +175,7 @@ export function GraphQLError( // eslint-disable-line no-redeclare
       value: originalError,
     },
     extensions: {
-      value: extensions,
+      value: extensions || (originalError && (originalError: any).extensions),
     },
   });
 

src/error/locatedError.js

@@ -33,6 +33,5 @@ export function locatedError(
     originalError && (originalError: any).positions,
     path,
     originalError,
-    originalError && (originalError: any).extensions,
   );
 }