MFC r326028:iconv: Fix a pointer mismatch.Catch NULL pointer earlier, check for empty string later.Apparently this fixes a GCC8 warning.Obtained from: NetBSD (CVS Rev. 1.21, 1.22) through DragonFlyBSD
MFC r275805:Fix incorrect type of "invalids" argument in __iconv() prototype.MFC r281550,281591:Remove the const qualifier from iconv(3) to comply with POSIX:http://pubs.opengroup.org/onlinepubs/9699919799/functions/iconv.htmlAdjust all code that calls iconv.PR: 199099