patch 8.2.4899: with latin1 encoding CTRL-W might go before the cmdline

Problem:    With latin1 encoding CTRL-W might go before the start of the
            command line.
Solution:   Check already being at the start of the command line.

src/ex_getln.c

@@ -1082,10 +1082,13 @@ cmdline_erase_chars(
 	{
 	    while (p > ccline.cmdbuff && vim_isspace(p[-1]))
 		--p;
-	    i = vim_iswordc(p[-1]);
-	    while (p > ccline.cmdbuff && !vim_isspace(p[-1])
-		    && vim_iswordc(p[-1]) == i)
-		--p;
+	    if (p > ccline.cmdbuff)
+	    {
+		i = vim_iswordc(p[-1]);
+		while (p > ccline.cmdbuff && !vim_isspace(p[-1])
+			&& vim_iswordc(p[-1]) == i)
+		    --p;
+	    }
 	}
 	else
 	    --p;

src/testdir/test_cmdline.vim

@@ -773,6 +773,9 @@ func Test_cmdline_remove_char()
 
     call feedkeys(":abc def\<S-Left>\<C-U>\<C-B>\"\<CR>", 'tx')
     call assert_equal('"def', @:, e)
+
+    " This was going before the start in latin1.
+    call feedkeys(": \<C-W>\<CR>", 'tx')
   endfor
 
   let &encoding = encoding_save

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4899,
 /**/
     4898,
 /**/