Fix option values that include =

[Opisek]

Why

Options that include = inside their value would break, in particular langmaps:
set langmap=ab,cd,=e should remap = to e, instead the option value was cut early at ab,cd,.

What changed

Merge all parts of the split string string but the first one using =.

Test plan

• :set langmap==j
• =
• Evaluate whether the cursor has moved down by one line

[nightwing]

Thank you!