Fix build on archs where char is unsigned

[m-hennecke]

For architectures that have char defined as unsigned char comparing char with negative numbers will always be false. Use explicit signed char to fix this.

When building xmpp on a system running OpenBSD/aarch64 a lot of compiler errors show up like these:

jid.c:84:8: warning: overflow converting case value to switch condition type (-12 to 244) [-Wswitch]        
                case -12: goto tr7;

or

jid.c:94:12: warning: result of comparison of constant -15 with expression of type 'char' is always false [-
Wtautological-constant-out-of-range-compare]                                                                        if ( (*p) < -15 ) {                                                                                 
             ~~~~ ^ ~~~

Which makes sense, because the char type on OpenBSD/aarch64 architecture defaults to unsigned char. For architectures having char defined as signed this changes nothing function wise.

[coveralls]

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Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
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Totals
Change from base Build 93:	0.0%
Covered Lines:	0
Relevant Lines:	18707

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💛 - Coveralls

[prefiks]

Thank you