fix setfiles segfault caused by libselinux-1.22

[Andreas Steinmetz <ast@domdv.de>]

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setfiles does reset user defined functions by calling the related setup
function with NULL as argument. Instead of resetting to the default
these setup functions did set up NULL as the function pointer. Fix attached.
-- 
Andreas Steinmetz                       SPAMmers use robotrap@domdv.de

[-- Attachment #2: libselinux-1.22.diff --]
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--- libselinux-1.22.orig/src/matchpathcon.c	2005-04-04 15:01:14.000000000 +0200
+++ libselinux-1.22/src/matchpathcon.c	2005-04-04 15:01:23.000000000 +0200
@@ -29,7 +29,10 @@
 
 void set_matchpathcon_printf(void (*f)(const char *fmt, ...))
 {
-	myprintf = f;
+	if (f)
+		myprintf = f;
+	else
+		myprintf = &default_printf;
 }
 
 static int default_invalidcon(const char *path, unsigned lineno, char *context)
@@ -45,7 +48,10 @@
 
 void set_matchpathcon_invalidcon(int (*f)(const char *p, unsigned l, char *c))
 {
-	myinvalidcon = f;
+	if (f)
+		myinvalidcon = f;
+	else
+		myinvalidcon = &default_invalidcon;
 }
 
 /*