Disable ligature checkbox for blacklisted fonts.

sources/PTYFontInfo.h

@@ -39,4 +39,8 @@
 @interface NSFont(PTYFontInfo)
 @property (nonatomic, readonly) BOOL it_defaultLigatures;
+
+// 0 means ligatures are not supported at all for this font.
+@property (nonatomic, readonly) NSInteger it_ligatureLevel;
+
 @end

sources/ProfilesTextPreferencesViewController.m

@@ -252,6 +252,9 @@ static NSInteger kNonAsciiFontButtonTag = 1;
     if (self.normalFont.it_defaultLigatures) {
         _asciiLigatures.state = NSOnState;
         _asciiLigatures.enabled = NO;
+    } else if (self.normalFont.it_ligatureLevel == 0) {
+        _asciiLigatures.state = NSOffState;
+        _asciiLigatures.enabled = NO;
     } else {
         _asciiLigatures.state = [self boolForKey:KEY_ASCII_LIGATURES] ? NSOnState : NSOffState;
         _asciiLigatures.enabled = YES;
@@ -259,6 +262,9 @@ static NSInteger kNonAsciiFontButtonTag = 1;
     if (self.nonAsciiFont.it_defaultLigatures) {
         _nonAsciiLigatures.state = NSOnState;
         _nonAsciiLigatures.enabled = NO;
+    } else if (self.nonAsciiFont.it_ligatureLevel == 0) {
+        _nonAsciiLigatures.state = NSOffState;
+        _nonAsciiLigatures.enabled = NO;
     } else {
         _nonAsciiLigatures.state = [self boolForKey:KEY_NON_ASCII_LIGATURES] ? NSOnState : NSOffState;
         _nonAsciiLigatures.enabled = YES;