patch 9.0.0947: invalid memory access in substitute with function

Problem:    Invalid memory access in substitute with function that goes to
            another file.
Solution:   Check for text locked in CTRL-W gf.

src/proto/normal.pro

@@ -1,4 +1,5 @@
 /* normal.c */
+int check_text_or_curbuf_locked(oparg_T *oap);
 void normal_cmd(oparg_T *oap, int toplevel);
 void check_visual_highlight(void);
 void end_visual_mode(void);