Small PR tweaks

Author: NWilson

src/pcre2_compile.c

@@ -1277,7 +1277,7 @@ if (allow_sign >= 0 && sign != 0)
     }
 
   if (sign > 0) n += allow_sign;
-  else if ((int)n > allow_sign)
+  else if (n > (uint32_t)allow_sign)
     {
     *errorcodeptr = ERR15;  /* Non-existent subpattern */
     goto EXIT;
@@ -3650,10 +3650,12 @@ while (ptr < ptrend)
       goto FAILED;
       }
 
-    /* Jump here from '(?[...])'. */
-
     class_mode_state = ((options & PCRE2_ALT_EXTENDED_CLASS) != 0)?
         CLASS_MODE_ALT_EXT : CLASS_MODE_NORMAL;
+
+    /* Jump here from '(?[...])'. That jump must initialize class_mode_state,
+    set c to the '[' character, and ptr to just after the '['. */
+
     FROM_PERL_EXTENDED_CLASS:
     okquantifier = TRUE;
 
@@ -4947,12 +4949,7 @@ while (ptr < ptrend)
           (IS_DIGIT(*ptr))? -1:(int)(cb->bracount), /* + and - are relative */
           MAX_GROUP_NUMBER, ERR61,
           &i, &errorcode)) goto FAILED;
-      if (i < 0)  /* NB (?0) is permitted */
-        {
-        // XXX Can we change this block to be PCRE2_ASSERT(i >= 0)? How can read_number return a negative value?
-        errorcode = ERR15;   /* Unknown group */
-        goto FAILED_BACK;
-        }
+      PCRE2_ASSERT(i >= 0);  /* NB (?0) is permitted, represented by i=0 */
       if (ptr >= ptrend || *ptr != CHAR_RIGHT_PARENTHESIS)
         goto UNCLOSED_PARENTHESIS;