The `num_functions_` counter got incremented at the exit of
`ProcessFunctionBody`, and for some exits it did not get incremented
at all. This was incorrect, it has to get incremented for each call to
`ProcessFunctionBody`. With this CL, `num_functions_` gets called at
the beginning of the function.

R=clemensb@chromium.org

Bug: v8:12852
Change-Id: I554916a7217533234a82ba397c301b926ce86b99
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3811587
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82259}