Get rid of gcc -fanalyzer error (though it was probably a false positive).

ChangeLog

@@ -9,6 +9,10 @@ zero bytes, because sed varies a lot from system to system and has problems
 with binary zeros. This is from Bugzilla #2681. Patch from Jeremie 
 Courreges-Anglas via Nam Nguyen. This fixes RunGrepTest for OpenBSD.
 
+2. Compiling with gcc 10.2's -fanalyzer option showed up a hypothetical problem 
+with a NULL dereference. I don't think this case could ever occur in practice, 
+but I have put in a check in order to get rid of the compiler error.
+
 
 Version 10.36 04-December-2020
 ------------------------------

src/pcre2_auto_possess.c

@@ -7,7 +7,7 @@ and semantics are as close as possible to those of the Perl 5 language.
 
                        Written by Philip Hazel
      Original API code Copyright (c) 1997-2012 University of Cambridge
-          New API code Copyright (c) 2016-2020 University of Cambridge
+          New API code Copyright (c) 2016-2021 University of Cambridge
 
 -----------------------------------------------------------------------------
 Redistribution and use in source and binary forms, with or without
@@ -490,6 +490,7 @@ switch(c)
   list[2] = (uint32_t)(end - code);
   return end;
   }
+
 return NULL;    /* Opcode not accepted */
 }
 
@@ -1186,12 +1187,16 @@ for (;;)
     c = *repeat_opcode;
     if (c >= OP_CRSTAR && c <= OP_CRMINRANGE)
       {
-      /* end must not be NULL. */
-      end = get_chr_property_list(code, utf, ucp, cb->fcc, list);
+      /* The return from get_chr_property_list() will never be NULL when
+      *code (aka c) is one of the three class opcodes. However, gcc with 
+      -fanalyzer notes that a NULL return is possible, and grumbles. Hence we 
+      put in a check. */ 
        
+      end = get_chr_property_list(code, utf, ucp, cb->fcc, list);
       list[1] = (c & 1) == 0;
 
-      if (compare_opcodes(end, utf, ucp, cb, list, end, &rec_limit))
+      if (end != NULL &&
+          compare_opcodes(end, utf, ucp, cb, list, end, &rec_limit))
         {
         switch (c)
           {