Skip MeasuredTemplate placeables whose _draw left them incomplete

[takaqiao]

Summary

A MeasuredTemplate placeable can survive into canvasReady without this.template (its PIXI.Graphics) or a registered highlight layer:

• loadTexture rejects on a missing/failing fill texture and _draw aborts before this.template = this.addChild(new PIXI.Graphics()).
• The system migrated spell areas off MeasuredTemplate — PF2e v8 places Region documents instead, but legacy MeasuredTemplate documents from older PF2e versions are still present in scene data.
• The placeable was created in a state where the canvas hadn't finished initializing.

The bundle currently dereferences both unconditionally and throws on those.

Repro

Foundry v14 + PF2e v8 world with any legacy MeasuredTemplate documents in a scene. On scene activation:

Error thrown in hooked function '' for hook 'canvasReady'.
Cannot set properties of undefined (setting 'alpha')
  at d (tokenmagic.js:859:70)
  at Object._loadFilters (tokenmagic.js:848:6)
  at Object.fn (tokenmagic.js:1762:8)

And then on every pointer move once defaultTemplateOnHover is on:

Uncaught TypeError: Cannot set properties of undefined (setting 'alpha')
  at ia.<anonymous> (settings.js:425:25)

Changes

• _singleLoadFilters (module/tokenmagic.js): for the TEMPLATE branch, fetch _TMFXgetSprite() once and skip the alpha/tint assignments when it returns null/undefined. The REGION branch already guarded its sprite this way; this brings the template branch in line.
• defaultTemplateOnHover mousemove handler (module/settings.js): continue past templates whose template.template is missing, and past templates whose grid highlight layer didn't get registered (the previous expression hl.renderable = … crashed otherwise).

No behavioural change for templates that drew successfully — broken templates are simply skipped instead of taking down the canvasReady chain or the pointermove pipeline.

Test plan

• Foundry v13 (verified): templates with valid textures still get their filters loaded and their hover dimming applied.
• Foundry v14 + PF2e v8 with a scene containing legacy MeasuredTemplate documents: canvasReady completes without throwing, pointer moves don't spam errors, and any healthy templates in the same scene still behave normally.
• Re-create / re-draw a template at runtime and confirm filters apply once _draw finishes.