Fix some code scanning issues.

.github/codeql.yml

@@ -1,5 +1,6 @@
 paths-ignore:
   - testsuite
+  - testmxml.c
 
 query-filters:
   - exclude:
@@ -46,3 +47,6 @@ query-filters:
       id: cpp/nested-loops-with-same-variable
   - exclude:
       id: cpp/stack-address-escape
+  - exclude:
+      id: cpp/world-writable-file-creation
+

mxml-file.c

@@ -556,7 +556,7 @@ mxmlSaveIO(
   if (col > 0)
   {
     // Make sure the file ends with a newline...
-    if ((io_cb)(io_cbdata, "\n", 1) < 0)
+    if ((io_cb)(io_cbdata, "\n", 1) != 1)
       return (false);
   }
 
@@ -914,8 +914,6 @@ mxml_getc(mxml_options_t   *options,	// I  - Options
 	break;
   }
 
-//  MXML_DEBUG("mxml_getc: %c (0x%04x)\n", ch < ' ' ? '.' : ch, ch);
-
   if (mxml_bad_char(ch))
   {
     _mxml_error(options, "Bad control character 0x%02x not allowed by XML standard.", ch);

testmxml.c

@@ -57,7 +57,6 @@ main(int  argc,				// I - Number of command-line args
 			*tree,		// Element tree
 			*node;		// Node which should be in test.xml
   mxml_index_t		*ind;		// XML index
-  mxml_type_t		type;		// Node type
   char			buffer[16384];	// Save string
   const char		*text;		// Text string
   bool			whitespace;	// Whitespace before text string