Merge pull request #1955 from Rythoka/SUP-HandleDamage-fix

## What type of PR is this.
1. [x] Bug
2. [ ] Change
3. [ ] Enhancement

### What have you changed and why?
Follow up to #1948. Same changes made in the HandleDamage EH in fn_SUP_ASFRoutine.sqf and fn_SUP_gunshipSpawn.sqf.
    

### Please specify which Issue this PR Resolves.
closes #1938

### Please verify the following and ensure all checks are completed.

1. [x] Have you loaded the mission in LAN host?
2. [ ] Have you loaded the mission on a dedicated server?

### Is further testing or are further changes required?
1. [x] No
2. [ ] Yes (Please provide further detail below.)

### How can the changes be tested?
Steps: 

********************************************************
Notes:

A3-Antistasi/functions/Supports/fn_SUP_ASFRoutine.sqf

@@ -106,6 +106,7 @@ _strikePlane addEventHandler
                 };
             };
         };
+        nil; //HandleDamage must return Nothing for damage to apply normally.
     }
 ];
 

A3-Antistasi/functions/Supports/fn_SUP_gunshipSpawn.sqf

@@ -106,6 +106,7 @@ _strikePlane addEventHandler
         {
             _plane setVariable ["Retreat", true];
         };
+        nil; //HandleDamage must return Nothing for damage to apply normally.
     }
 ];