Check FontFamily null before adding it.

Missing ttf files under /product/fonts will cause NullPointerException.
This CL fixes it.

Bug: 187901462
Test: Flash Sabrina to Android S. Boot to check if there's still an error.
Change-Id: I9d39c2a6e4730563f35f43176f630ac0439767b3

graphics/java/android/graphics/fonts/FontCustomizationParser.java

@@ -134,7 +134,11 @@ public class FontCustomizationParser {
             throw new IllegalArgumentException("customizationType must be specified");
         }
         if (customizationType.equals("new-named-family")) {
-            out.add(FontListParser.readFamily(parser, fontDir, updatableFontMap, false));
+            FontFamily fontFamily = FontListParser.readFamily(
+                    parser, fontDir, updatableFontMap, false);
+            if (fontFamily != null) {
+                out.add(fontFamily);
+            }
         } else {
             throw new IllegalArgumentException("Unknown customizationType=" + customizationType);
         }