Update mailmap file [skip ci]
Fix system warning in gpc_get_string_array()

The fix for issue #17640 did not consider that the value returned by
gpc_get() is not necessarily an array - it can be the default value
(e.g. null) causing PHP to throw an 'Invalid argument supplied for
foreach()' warning.

Fixes #17967 (ported from 1.2.x)