Fix match in if-then-else branches expanding to vertical with fit-or-vertical (#2798) When a `match expr with` appeared as a branch of `if-then-else` with `if-then-else=fit-or-vertical`, the match keyword, scrutinee, and `with` were broken onto separate lines even when they easily fit on one line: if true then match expr with | true -> () | false -> () The regression was introduced by 8056fa50 ("Overhaul begin match formatting"), which changed `fmt_match` to wrap `pro` inside a nested `hvbox 0 (pro_inner $ keyword)`. When the match is inside an if-then-else branch, the `pro` carries a `break_unless_newline 1000 2` (from the Fit_or_vertical branch_pro). This inflates the inner hvbox's size to 1000+, causing the Format engine to classify the parent hovbox as non-fitting, which forces all breaks in the `match .. expr .. with` box to break. Fix: in `match_inner_pro`, return `false` for `Pexp_ifthenelse` context (same as already done for `Pexp_infix`), so that `pro` is placed outside the match's inner hvbox as `pro_outer`, where it does not interfere with the match keyword/expr/with fitting on one line.