Avoid potential read of bad address in CEA block processing

Detail:
  c/ScrModes - Reorder while loop conditions to ensure the DTD offset is checked before we try reading any data; prevents potential data abort if initial offset is too large to be valid.
Admin:
  Builds, untested


Version 0.47. Retagged as 'ScrModes-0_47'

c/ScrModes

@@ -2516,8 +2516,8 @@ static _kernel_oserror *process_cea_extension_type_3(EDIDExtensionBlockRef ext_b
         return NULL;
     }
 
-    while ((extdata[dtd_offset] != 0) && (extdata[dtd_offset+1] != 0) &&
-           (dtd_offset < (128 - 18)))
+    while ((dtd_offset < (128 - 18)) &&
+           (extdata[dtd_offset] != 0) && (extdata[dtd_offset+1] != 0))
     {
         ModeDescriptionRef mp;
         mp = (ModeDescriptionRef) malloc (sizeof(ModeDescription));