Make error checks on encoding methods for docomo, kddi, sb consistent

Some places use an if check, which implicitly checks for a non-zero
value, and some places use > 0. The > 0 is the correct one because at
least some of those functions already use the CK() macro to return -1 on
error. Because -1 != 0 this is wrongly interpreted as a success instead
of a failure.

Author: nielsdos

ext/mbstring/libmbfl/filters/mbfilter_iso2022jp_mobile.c

@@ -288,7 +288,7 @@ int mbfl_filt_conv_wchar_2022jp_mobile(int c, mbfl_convert_filter *filter)
 		}
 	}
 
-	if (mbfilter_unicode2sjis_emoji_kddi(c, &s1, filter)) {
+	if (mbfilter_unicode2sjis_emoji_kddi(c, &s1, filter) > 0) {
 		CODE2JIS(c1,c2,s1,s2);
 		s1 -= 0x1600;
 	}

ext/mbstring/libmbfl/filters/mbfilter_sjis_mobile.c

@@ -819,9 +819,9 @@ int mbfl_filt_conv_wchar_sjis_mobile(int c, mbfl_convert_filter *filter)
 		}
 	}
 
-	if ((filter->to == &mbfl_encoding_sjis_docomo && mbfilter_unicode2sjis_emoji_docomo(c, &s1, filter)) ||
-		  (filter->to == &mbfl_encoding_sjis_kddi   && mbfilter_unicode2sjis_emoji_kddi(c, &s1, filter)) ||
-		  (filter->to == &mbfl_encoding_sjis_sb     && mbfilter_unicode2sjis_emoji_sb(c, &s1, filter))) {
+	if ((filter->to == &mbfl_encoding_sjis_docomo && mbfilter_unicode2sjis_emoji_docomo(c, &s1, filter) > 0) ||
+		  (filter->to == &mbfl_encoding_sjis_kddi   && mbfilter_unicode2sjis_emoji_kddi(c, &s1, filter) > 0) ||
+		  (filter->to == &mbfl_encoding_sjis_sb     && mbfilter_unicode2sjis_emoji_sb(c, &s1, filter) > 0)) {
 		CODE2JIS(c1,c2,s1,s2);
  	}