patch 8.2.3486: illegal memory access with invalid sequence of commands

Problem:    Illegal memory access with invalid sequence of commands.
Solution:   Do not call leave_block() when not in a try block. (closes #8966)
            Reset did_emsg so that exception is shown as an error.

src/testdir/test_trycatch.vim

@@ -2295,5 +2295,25 @@ func Test_error_in_catch_and_finally()
   call delete('XtestCatchAndFinally')
 endfunc
 
+" This was causing an illegal memory access
+func Test_leave_block_in_endtry_not_called()
+  let lines =<< trim END
+      vim9script
+      try #
+      for x in []
+      if
+      endwhile
+      if
+      endtry
+  END
+  call writefile(lines, 'XtestEndtry')
+  try
+    source XtestEndtry
+  catch /E171:/
+  endtry
+
+  call delete('XtestEndtry')
+endfunc
+
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