win32: allow for vsnprintf returning -1

vsnprintf can return -1.  I've seen it do this when writing to a small
buffer while vsnprintf(NULL, 0, ...) returns a valid length.  I'd prefer
not to rely on the latter working with arbitrary old Windows runtimes
so just skip ANSI emulation if -1 is returned.

1 files changed, 6 insertions, 1 deletions

diff --git a/win32/winansi.c b/win32/winansi.c
index d61e8a2cf..c0493c77e 100644
--- a/win32/winansi.c
+++ b/win32/winansi.c
@@ -536,9 +536,14 @@ int winansi_vfprintf(FILE *stream, const char *format, va_list list)
                 if (!buf)
                         goto abort;
 
-                len = vsnprintf(buf, len + 1, format, list);
+                va_copy(cp, list);
+                len = vsnprintf(buf, len + 1, format, cp);
+                va_end(cp);
         }
 
+        if (len == -1)
+                goto abort;
+
         rv = ansi_emulate(buf, stream);
 
         if (buf != small_buf)