QtFRED: Fix crash in Ship Initial Status dialog when editing multiple ships

[LuytenFS]

Fixes a segfault I've stumbled upon when clicking OK in the Ship Initial Status dialog with more than one ship selected.

Cause
ShipInitialStatusDialogModel::initializeData() only sets up _numDockPoints and _dockpointArray when editing a single ship. In multi-edit mode _numDockPoints was left uninitialized (garbage value) and _dockpointArray stayed null. apply() still called updateDockingInfo(), which then indexed the null array.

Changes

• Give _numDockPoints (and _multiEdit) default initializers so the multi-edit state is well defined.
• Skip updateDockingInfo() in apply() when editing multiple ships, since docking is only editable for a single ship.
• Add a guard in updateDockingInfo() that returns early if there is no dock point data.

Testing

• Select multiple ships, open Initial Status, click OK: no crash (previously SIGSEGV in updateDockingInfo).
• Single ship with dock points: docking changes still apply as before.

Additionally I noticed a triple copy-paste where the shield and hull "blank field" checks tested vflag three times instead of hflag, sflag. I assumed that wasn't intentionally, so correct me on this one.

Here's the backtrace using GDB if its of any use:
backtrace.txt