Fix oversight in DFA when changing OP_REVERSE; also add some unrelated tests

Author: PhilipHazel

src/pcre2_dfa_match.c

@@ -591,7 +591,7 @@ if (*this_start_code == OP_ASSERTBACK || *this_start_code == OP_ASSERTBACK_NOT)
   end_code = this_start_code;
   do
     {
-    size_t back = (size_t)GET(end_code, 2+LINK_SIZE);
+    size_t back = (size_t)GET2(end_code, 2+LINK_SIZE);
     if (back > max_back) max_back = back;
     end_code += GET(end_code, 1);
     }

testdata/testinput2

@@ -5988,6 +5988,12 @@ a)"xI
 
 /(?<!( {65054}){9,44965})/
 
+/(?(?<!|(|a)))/
+    aaaa\=get=0
+
+/(?(?<!|a?))/
+    aaaa\=get=0
+
 # --------
 
 /(?<=(()()()()()()()()()()()()()(()()()()(())()()()()(()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()(())()()()()(()()()()()()(()()()()()()()()()()()()()()()()()()()()()(())()()()()(()()()()()()()()()()()()()(()()()()()()()()()()()()()(()())))))))))/

testdata/testoutput2

@@ -17821,6 +17821,16 @@ Failed: error 200 at offset 5: branch too long in variable-length lookbehind ass
 /(?<!( {65054}){9,44965})/
 Failed: error 187 at offset 0: lookbehind assertion is too long
 
+/(?(?<!|(|a)))/
+    aaaa\=get=0
+ 0: 
+ 0G  (0)
+
+/(?(?<!|a?))/
+    aaaa\=get=0
+ 0: 
+ 0G  (0)
+
 # --------
 
 /(?<=(()()()()()()()()()()()()()(()()()()(())()()()()(()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()(())()()()()(()()()()()()(()()()()()()()()()()()()()()()()()()()()()(())()()()()(()()()()()()()()()()()()()(()()()()()()()()()()()()()(()())))))))))/