patch 8.2.3946: when an internal error makes Vim exit the error is not seen

Problem:    When an internal error makes Vim exit the error is not seen.
Solution:   Add the error to the test output.

src/message.c

@@ -824,11 +824,14 @@ semsg(const char *s, ...)
 iemsg(char *s)
 {
     if (!emsg_not_now())
+    {
 	emsg_core((char_u *)s);
 #ifdef ABORT_ON_INTERNAL_ERROR
+	set_vim_var_string(VV_ERRMSG, (char_u *)s, -1);
 	abort();
 #endif
     }
+}
 
 #ifndef PROTO  // manual proto with __attribute__
 /*

src/testdir/runtest.vim

@@ -304,6 +304,7 @@ endfunc
 func EarlyExit(test)
   " It's OK for the test we use to test the quit detection.
   if a:test != 'Test_zz_quit_detected()'
+    call add(v:errors, v:errmsg)
     call add(v:errors, 'Test caused Vim to exit: ' . a:test)
   endif
 

src/version.c

@@ -749,6 +749,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3946,
 /**/
     3945,
 /**/