patch 8.2.4174: Vim9: can use an autoload name in normal script

Problem:    Vim9: can use an autoload name in normal script.
Solution:   Disallow using an autoload name.

src/errors.h

@@ -3209,7 +3209,8 @@ EXTERN char e_cannot_import_dot_vim_without_using_as[]
 	INIT(= N_("E1261: Cannot import .vim without using \"as\""));
 EXTERN char e_cannot_import_same_script_twice_str[]
 	INIT(= N_("E1262: Cannot import the same script twice: %s"));
-// E1263 unused
+EXTERN char e_using_autoload_name_in_non_autoload_script_str[]
+	INIT(= N_("E1263: Using autoload name in a non-autoload script: %s"));
 EXTERN char e_autoload_import_cannot_use_absolute_or_relative_path[]
 	INIT(= N_("E1264: Autoload import cannot use absolute or relative path: %s"));
 EXTERN char e_cannot_use_partial_here[]

src/testdir/test_vim9_import.vim

@@ -1622,6 +1622,18 @@ def Test_autoload_missing_function_name()
   delete('Xdir', 'rf')
 enddef
 
+def Test_autoload_name_wring()
+  var lines =<< trim END
+     vim9script
+     def Xscriptname#Func()
+     enddef
+  END
+  writefile(lines, 'Xscriptname.vim')
+  CheckScriptFailure(lines, 'E1263:')
+
+  delete('Xscriptname')
+enddef
+
 def Test_import_autoload_postponed()
   mkdir('Xdir/autoload', 'p')
   var save_rtp = &rtp

src/userfunc.c

@@ -4495,6 +4495,12 @@ define_function(exarg_T *eap, char_u *name_arg, garray_T *lines_to_free)
 		    }
 		}
 	    }
+	    else if (vim9script && vim_strchr(name, AUTOLOAD_CHAR) != NULL)
+	    {
+		semsg(_(e_using_autoload_name_in_non_autoload_script_str),
+									 name);
+		goto erret;
+	    }
 	}
 	if (var_conflict)
 	{

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4174,
 /**/
     4173,
 /**/