GPencil: Scripting weight_get and Vertex Groups not working at expected with several groups #91511

System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 960M/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 391.25

Blender Version
Broken: version: 2.93.1, branch: master, commit date: 2021-06-22 05:57, hash: 1b8d33b18cGreasepencil weight_get and vertex_group.blend

Short description of error

weight_get will result in a vertex_group index error (RuntimeError: Error: Groups: index out of range) even when the stroke is weight-painted completely
Running weight_set along stroke first, weight-painting manually, and then running weight_get will not throw the error (most of the time).
The vertex_group index property of weight_get will result in a (RuntimeError: Error: Groups: index out of range) if a lower vertex_group index property had resulted in an index out of range error.

Exact steps for others to reproduce the error
See attached blend.

I've included 3 examples:
A try and except script to get the vertex weight of 4 strokes which fails on 3 upper vertex group indices.
A script that sets the vertex weight of all points to 0 and after which when you weight paint manually and rerun the first script, you get the vertex weight successfully
A script where you create the vertex_group and set them with a specific value successfully, but when you try to read them back with weight_get, it results with a vertex group index out of range

Added subscriber: @kluya

Added subscriber: @antoniov

Changed status from 'Needs Triage' to: 'Confirmed'

The problem is checking the number of available weights.

This issue was referenced by cc31c159a1

This issue was referenced by 1f51672d71

Changed status from 'Confirmed' to: 'Resolved'

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GPencil: Scripting weight_get and Vertex Groups not working at expected with several groups #91511