lib: Address GCC 11.2.1 compiler warning
Symptom was:
In file included from xmltok.c:58:
xmltok_ns.c: In function ‘findEncodingNS’:
xmltok.h:276:10: warning: ‘buf’ may be used uninitialized [-Wmaybe-uninitialized]
276 | (((enc)->utf8Convert)(enc, fromP, fromLim, toP, toLim))
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
xmltok_ns.c:99:3: note: in expansion of macro ‘XmlUtf8Convert’
99 | XmlUtf8Convert(enc, &ptr, end, &p, p + ENCODING_MAX - 1);
| ^~~~~~~~~~~~~~
xmltok.h:276:10: note: by argument 5 of type ‘const char *’ to ‘enum XML_Convert_Result(const ENCODING *, const char **, const char *, char **, const char *)’ {aka ‘enum XML_Convert_Result(const struct encoding *, const char **, const char *, char **, const char *)’}
276 | (((enc)->utf8Convert)(enc, fromP, fromLim, toP, toLim))
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
xmltok_ns.c:99:3: note: in expansion of macro ‘XmlUtf8Convert’
99 | XmlUtf8Convert(enc, &ptr, end, &p, p + ENCODING_MAX - 1);
| ^~~~~~~~~~~~~~
In file included from xmltok.c:1666:
xmltok_ns.c:96:8: note: ‘buf’ declared here
96 | char buf[ENCODING_MAX];
| ^~~
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