Avoid memory leaks from file selection

https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=17106

src/libopensc/card-mcrd.c

@@ -836,6 +836,9 @@ select_file_by_path(sc_card_t * card, unsigned short *pathptr,
 			priv->curpathlen--;
 			priv->is_ef = 0;
 		}
+		/* Free the previously allocated file so we do not leak memory here */
+		sc_file_free(*file);
+		*file = NULL;
 		r = select_down(card, pathptr, pathlen, 0, file);
 	}
 	return r;