Fix other file visitor to handle incremental analysis properly

The other file visitor would unconditionally scan the full
project contents for each scope, even when project.getSubset()
(used for incremental analysis in IDEs) was non null.

Also avoid NPE when lint is scanning a java file without a
package declaration.

Change-Id: I74e813b41c2e32acac879b277dc974619156adbd
3 files changed