Fix unnecessary overallocation due to incomplete character

When incomplete characters are found at the end of a string the
code ran amok and allocated lots of memory.  Stricter limits
are now in place.

posix/bug-regex32.c

@@ -0,0 +1,36 @@
+// BZ 12811
+#include <regex.h>
+#include <stdio.h>
+#include <locale.h>
+
+static int
+do_test (void)
+{
+  char buf[1000];
+  regex_t preg;
+  if (setlocale (LC_CTYPE, "de_DE.UTF-8") == NULL)
+    {
+      puts ("setlocale failed");
+      return 1;
+    }
+
+  int e = regcomp (&preg, ".*ab", REG_ICASE);
+  if (e != 0)
+    {
+      regerror (e, &preg, buf, sizeof (buf));
+      printf ("regcomp = %d \"%s\"\n", e, buf);
+      return 1;
+    }
+
+  // Incomplete character at the end of the buffer
+  e = regexec (&preg, "aaaaaaaaaaaa\xc4", 0, NULL, 0);
+
+  regfree (&preg);
+  regerror (e, &preg, buf, sizeof (buf));
+  printf ("regexec = %d \"%s\"\n", e, buf);
+
+  return e != REG_NOMATCH;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"