say: Don't prepend ampersand erroneously.

say: Don't prepend ampersand erroneously.

Some logic in say.c for determining if we need
to also add an ampersand for file seperation was faulty,
as non-successful files would increment the count, causing
a leading ampersand to be added improperly.

This is fixed, and a unit test that captures this regression
is also added.

ASTERISK-30248 #close

Change-Id: I02c1d3a11d82fe4ea8b462070cbd1effb5834d2b