patch 9.1.1316: missing memory allocation failure in os_mswin.c

Problem:  missing memory allocation failure in os_mswin.c
Solution: check for memory allocation failure and return early.
          (John Marriott)

closes: #17134

Signed-off-by: John Marriott <basilisk@internode.on.net>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/proto/os_mswin.pro b/src/proto/os_mswin.pro
index 055cf8c..e8e08d2 100644
--- a/src/proto/os_mswin.pro
+++ b/src/proto/os_mswin.pro
@@ -1,4 +1,5 @@
 /* os_mswin.c */
+void SaveInst(HINSTANCE hInst);
 void mch_exit_g(int r);
 void mch_early_init(void);
 int mch_input_isatty(void);