patch 9.0.1556: Vim9: error for missing "return" after "throw"

Problem:    Vim9: error for missing "return" after "throw".
Solution:   Set had_return flag for "throw". (closes #12262)

src/testdir/test_vim9_func.vim

@@ -488,6 +488,19 @@ def Test_missing_return()
                    'enddef'], 'E1095:')
 enddef
 
+def Test_not_missing_return()
+  var lines =<< trim END
+      def Funky(): number
+        if false
+          return 0
+        endif
+        throw 'Error'
+      enddef
+      defcompile
+  END
+  v9.CheckScriptSuccess(lines)
+enddef
+
 def Test_return_bool()
   var lines =<< trim END
       vim9script

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1556,
 /**/
     1555,
 /**/

src/vim9compile.c

@@ -3611,6 +3611,7 @@ compile_def_function(
 		    break;
 	    case CMD_throw:
 		    line = compile_throw(p, &cctx);
+		    cctx.ctx_had_return = TRUE;
 		    break;
 
 	    case CMD_eval: