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/quickfix.c

@@ -7078,7 +7078,7 @@ wipe_dummy_buffer(buf_T *buf, char_u *dirname_start)
 		    break;
 		}
 	if (!did_one)
-	    return;
+	    goto fail;
     }
 
     if (curbuf != buf && buf->b_nwindows == 0)	// safety check
@@ -7102,7 +7102,13 @@ wipe_dummy_buffer(buf_T *buf, char_u *dirname_start)
 	if (dirname_start != NULL)
 	    // When autocommands/'autochdir' option changed directory: go back.
 	    restore_start_dir(dirname_start);
+
+	return;
     }
+
+fail:
+    // Keeping the buffer, remove the dummy flag.
+    buf->b_flags &= ~BF_DUMMY;
 }
 
 /*

src/testdir/test_quickfix.vim

@@ -6921,4 +6921,23 @@ func Test_vimgrep_dummy_buffer_crash()
   %bw!
 endfunc
 
+func Test_vimgrep_dummy_buffer_keep()
+  augroup DummyKeep
+    autocmd!
+    " Trigger a wipe of the dummy buffer by aborting script processing. Prevent
+    " wiping it by splitting it from the autocmd window into an only window.
+    autocmd BufReadCmd * ++once let s:dummy_buf = bufnr()
+          \| tab split | call interrupt()
+  augroup END
+
+  call assert_fails('vimgrep /./ .')
+  call assert_equal(1, bufexists(s:dummy_buf))
+  " Ensure it's no longer considered a dummy; should be able to switch to it.
+  execute s:dummy_buf 'sbuffer'
+
+  unlet! s:dummy_buf
+  autocmd! DummyKeep
+  %bw!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

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