patch 8.2.3759: quickfix buffer becomes hidden while still in a window

Problem:    Quickfix buffer becomes hidden while still in a window.
Solution:   Check if the closed window is the last window showing the quickfix
            buffer. (Yegappan Lakshmanan, closes #9303, closes #9300)
diff --git a/src/window.c b/src/window.c
index 4050ed0..47fb815 100644
--- a/src/window.c
+++ b/src/window.c
@@ -2433,8 +2433,10 @@
 #endif
 
 #ifdef FEAT_QUICKFIX
-    // When the quickfix/location list window is closed, unlist the buffer.
-    if (win->w_buffer != NULL && bt_quickfix(win->w_buffer))
+    // When a quickfix/location list window is closed and the buffer is
+    // displayed in only one window, then unlist the buffer.
+    if (win->w_buffer != NULL && bt_quickfix(win->w_buffer)
+					&& win->w_buffer->b_nwindows == 1)
 	win->w_buffer->b_p_bl = FALSE;
 #endif