MigrateConfig: stop duplicating options that have an empty value in the template

[Cybis320]

Problem

MigrateConfig writes a duplicate entry for any option whose template value is empty, producing a .config that RMS cannot read:

[Build]

; Compiler arguments for cython
rpi_weave: -O3 -mfpu=neon -funsafe-loop-optimizations -ftree-loop-if-convert-stores
linux_pc_weave: -O3
win_pc_weave:

; The following options were preserved but are not in the template
win_pc_weave: -Wall

configparser then raises DuplicateOptionError and RMS crashes on startup.

Two options in the template have empty values, and both are affected:

• time_server: (.config:62)
• win_pc_weave: (.config:392)

Cause

Attribute lines were parsed with re.split(": ", l), which requires a colon followed by a space. Lines with an empty value do not match, so in the template merge loop they took the cnt != 2 branch: the template line was written out verbatim and the key was never removed from attributes_dict. It then fell through to the "unrecognized attributes preserved" step, where the option is valid per ConfigReader.py, so it was appended a second time.

The crash only shows up when the user's config has a non-empty value for one of these options, which is why it went unnoticed.

Fix

• New parseAttributeLine() helper using ^([^:]+?)\s*:\s*(.*)$, replacing both re.split(": ", ...) sites. It handles empty values and makes the space after the colon optional — linux_pc_weave:-O2 was previously dropped silently, losing the user's setting.
• Preserved empty values are written without a trailing space (rpi_weave:, not rpi_weave: ).
• Added a duplicate guard in the preserve step: options already present in the new config are skipped (matched case-insensitively, as configparser does). This backstops the same crash from any other parse gap or case mismatch.

Testing

• Repro before the fix: duplicate win_pc_weave/time_server, DuplicateOptionError. After: values kept in place, config parses, win_pc_weave = '-Wall'.
• Recovery: running the fixed migrator over an already-corrupted config heals it — it warns duplicate value for win_pc_weave, assuming last value, keeps -Wall, and emits a single valid entry. Affected stations can just re-run python -m Utils.MigrateConfig -u.
• Identity test (repo .config migrated against itself) is byte-identical apart from the added ; Reformated by footer — no drift across the other 190 attributes.
• Edge cases covered: user-cleared value, no space after the colon, and values containing colons (device: rtsp://...).

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