[gnome-mines] Fix timer not stopping when game ends via multi-release

[Robert Roth <robertroth src gnome org>]

commit 1ede3f7750ba45aad8724c280aa5f8c851c195eb
Author: Christian <christian guinard dal ca>
Date:   Mon Oct 5 14:21:10 2020 -0300

    Fix timer not stopping when game ends via multi-release

 src/minefield.vala | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)
---
diff --git a/src/minefield.vala b/src/minefield.vala
index 8702a1a..faf92e3 100644
--- a/src/minefield.vala
+++ b/src/minefield.vala
@@ -207,10 +207,13 @@ public class Minefield : Object
             if (!is_location (nx, ny))
                 continue;
 
-            if (do_clear && get_flag (nx, ny) != FlagType.FLAG)
+            if (do_clear && get_flag (nx, ny) != FlagType.FLAG){
                 clear_mine (nx, ny);
-            else
+                if (clock == null)
+                    return;
+            } else {
                 set_flag (nx, ny, FlagType.FLAG);
+            }
         }
     }