Don't show warnings for fonts not bundled.

The extended font set, used on Nexus 5, new Nexus 7 etc., uses OpenType
CFF fonts which don't work well with Java. These fonts are deliberately
excluded from the SDK build.

This change skips the warnings for the missing fonts. However, we still
show warnings for other fonts that failed to load. If the set of fonts
bundled with the SDK changes, we will need to update the list of missing
fonts in FontFamily_Delegate.java.

Change-Id: I3197b5350d048daa09512e8024188909179b1799