Deny nil outputpaths

To prevent nils from permeating the rest of the codebase.

Bug: 379329165
Test: m nothing --no-skip-soong-tests
Change-Id: I3e789b6af0f101cf4bc0bd4666bf3a443f2f2c84
diff --git a/android/prebuilt_test.go b/android/prebuilt_test.go
index 5e4af0b..b90ef3b 100644
--- a/android/prebuilt_test.go
+++ b/android/prebuilt_test.go
@@ -508,11 +508,10 @@
 }
 
 func (p *prebuiltModule) GenerateAndroidBuildActions(ctx ModuleContext) {
-	var src Path
 	if len(p.properties.Srcs) >= 1 {
-		src = p.prebuilt.SingleSourcePath(ctx)
+		src := p.prebuilt.SingleSourcePath(ctx)
+		ctx.SetOutputFiles(Paths{src}, "")
 	}
-	ctx.SetOutputFiles(Paths{src}, "")
 }
 
 func (p *prebuiltModule) Prebuilt() *Prebuilt {