[pshinter] Fully initialize globals->blues.

These defaults may be overriden later by `psh_blues_scale_zones` which
is conditionally called from `psh_globals_set_scale`.

* src/pshinter/pshglob.c (psh_globals_new): initialize
`blues->blue_threshold` and `blues->no_overshoots`.

Fixes: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=43701
12 jobs for fully_initialize_globals_blues in 9 minutes and 36 seconds (queued for 2 seconds)
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