Code review comment for lp:~macslow/notify-osd/fix-425508

Made bubble_append_message_body() avoid accidentally calling g_free() on an uninitialized pointer (text). pango_parse_markup() can leave text untouched, so later on g_free() would fail without initializing text to NULL correctly. Also made tests results more robust. This is meant to fix LP: #425508 and its duplicates...

LP: #426230
LP: #427129
LP: #429025