Allow libraries with no sources to be installed

Libraries with no source files but static lib dependencies should
still be installable.

Test: m -j checkbuild
Change-Id: Ibc91aa3153241092ce86888dbf90e99b66069ff2

java/java.go

@@ -527,7 +527,7 @@ func (j *Module) compile(ctx android.ModuleContext) {
 	j.classpathFile = outputFile
 
 	// TODO(ccross): handle hostdex
-	if ctx.Device() && len(srcFiles) > 0 && j.installable() {
+	if ctx.Device() && j.installable() {
 		dxFlags := j.deviceProperties.Dxflags
 		if false /* emma enabled */ {
 			// If you instrument class files that have local variable debug information in