bound WKB point reads to the Z/M byte stride in mappostgis - #7593

What does this PR do?

AddressSanitizer, reading a Z LineString whose point count clears the old check:

READ of size 8 at 0x6070000000d4 thread T0
    #0 wkbReadPointP
0x6070000000d4 is located 0 bytes after 68-byte region

wkbReadLine bounds the point count against the bytes left divided by 16, but wkbReadPointP reads 24 bytes per point for a Z or M geometry and 32 for ZM, so a Z/M linestring or polygon ring can read past the WKB buffer returned by a PostGIS query. arcStrokeCircularString had no such check at all and read its whole odd point count unbounded. Both now derive the per-point stride from the Z/M flags before reading. wkbReadLine also clears the lineObj on the reject path, since msAddLineDirectly takes ownership of line->point and the early return previously left it uninitialized.

What are related issues/pull requests?

None.

AI tool usage

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Tasklist

• Make sure code is correctly formatted (cf pre-commit configuration)
• Add test case(s) in /msautotest (follow steps in Regression Testing)
• Add documentation
• Review
• Adjust for comments
• All CI builds and checks have passed