patch 8.2.3364: Vim9: crash when :for is skipped

Problem:    Vim9: crash when :for is skipped.
Solution:   Skip more code generation. (Naruhiko Nishino, closes #8777)

src/testdir/test_vim9_script.vim

@@ -2552,6 +2552,70 @@ def Test_for_outside_of_function()
   delete('Xvim9for.vim')
 enddef
 
+def Test_for_skipped_block()
+  # test skipped blocks at outside of function
+  var lines =<< trim END
+    var result = []
+    if true
+      for n in [1, 2]
+        result += [n]
+      endfor
+    else
+      for n in [3, 4]
+        result += [n]
+      endfor
+    endif
+    assert_equal([1, 2], result)
+
+    result = []
+    if false
+      for n in [1, 2]
+        result += [n]
+      endfor
+    else
+      for n in [3, 4]
+        result += [n]
+      endfor
+    endif
+    assert_equal([3, 4], result)
+  END
+  CheckDefAndScriptSuccess(lines)
+
+  # test skipped blocks at inside of function
+  lines =<< trim END
+    def DefTrue()
+      var result = []
+      if true
+        for n in [1, 2]
+          result += [n]
+        endfor
+      else
+        for n in [3, 4]
+          result += [n]
+        endfor
+      endif
+      assert_equal([1, 2], result)
+    enddef
+    DefTrue()
+
+    def DefFalse()
+      var result = []
+      if false
+        for n in [1, 2]
+          result += [n]
+        endfor
+      else
+        for n in [3, 4]
+          result += [n]
+        endfor
+      endif
+      assert_equal([3, 4], result)
+    enddef
+    DefFalse()
+  END
+  CheckDefAndScriptSuccess(lines)
+enddef
+
 def Test_for_loop()
   var lines =<< trim END
       var result = ''

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3364,
 /**/
     3363,
 /**/

src/vim9compile.c

@@ -8041,6 +8041,8 @@ compile_for(char_u *arg_start, cctx_T *cctx)
     }
     arg_end = arg;
 
+    if (cctx->ctx_skip != SKIP_YES)
+    {
 	// If we know the type of "var" and it is a not a supported type we can
 	// give an error now.
 	vartype = ((type_T **)stack->ga_data)[stack->ga_len - 1];
@@ -8187,6 +8189,7 @@ compile_for(char_u *arg_start, cctx_T *cctx)
 	    generate_instr_debug(cctx);
 	    cctx->ctx_prev_lnum = save_prev_lnum;
 	}
+    }
 
     return arg_end;
 
@@ -8217,6 +8220,8 @@ compile_endfor(char_u *arg, cctx_T *cctx)
     }
     forscope = &scope->se_u.se_for;
     cctx->ctx_scope = scope->se_outer;
+    if (cctx->ctx_skip != SKIP_YES)
+    {
 	unwind_locals(cctx, scope->se_local_count);
 
 	// At end of ":for" scope jump back to the FOR instruction.
@@ -8232,6 +8237,7 @@ compile_endfor(char_u *arg, cctx_T *cctx)
 	// Below the ":for" scope drop the "expr" list from the stack.
 	if (generate_instr_drop(cctx, ISN_DROP, 1) == NULL)
 	    return NULL;
+    }
 
     vim_free(scope);