Change how canceled attacks are recorded (#1480)

## Description:

Minor fix:
The `retreat()` function is called everytime the troops have to come
back home:
- alliance between the belligerents
- cluster / player conquest
- canceled attack

Each of those cases are recorded as "canceled" but only the actually
canceled attacks should be recorded as such.


## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I have read and accepted the CLA aggreement (only required once).

## Please put your Discord username so you can be contacted if a bug or
regression is found:

IngloriousTom

src/core/execution/AttackExecution.ts

@@ -185,8 +185,11 @@ export class AttackExecution implements Execution {
     this.attack.delete();
     this.active = false;
 
-    // Record stats
-    this.mg.stats().attackCancel(this._owner, this.target, survivors);
+    // Not all retreats are canceled attacks
+    if (this.attack.retreated()) {
+      // Record stats
+      this.mg.stats().attackCancel(this._owner, this.target, survivors);
+    }
   }
 
   tick(ticks: number) {