patch 9.1.1376: quickfix dummy buffer may remain as dummy buffer

Problem:  when failing to wipeout a quickfix dummy buffer, it will
          remain as a dummy buffer, despite being kept.
Solution: clear its dummy BF_DUMMY flag in this case (Sean Dewar).

closes: #17283

Signed-off-by: Sean Dewar <6256228+seandewar@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1376,
 /**/
     1375,
 /**/