cc/cc.go: Harden GetSnapshot() against nil pointer panic

* Retrieve SnapshotInfo only if the calling module is device-variant.
* Test for nil-ness before calling ctx.OtherModuleProvider().

Bug: 192647618
Test: Presubmit
Change-Id: Ida8582f756e1b15f8c14c816ed6e736b47995877
diff --git a/cc/cc.go b/cc/cc.go
index 15cb39a..af224e9 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -2065,9 +2065,9 @@
 }
 
 func GetSnapshot(c LinkableInterface, snapshotInfo **SnapshotInfo, actx android.BottomUpMutatorContext) SnapshotInfo {
-	// Only modules with BOARD_VNDK_VERSION uses snapshot.  Others use the zero value of
+	// Only device modules with BOARD_VNDK_VERSION uses snapshot.  Others use the zero value of
 	// SnapshotInfo, which provides no mappings.
-	if *snapshotInfo == nil {
+	if *snapshotInfo == nil && c.Device() {
 		// Only retrieve the snapshot on demand in order to avoid circular dependencies
 		// between the modules in the snapshot and the snapshot itself.
 		var snapshotModule []blueprint.Module
@@ -2076,16 +2076,16 @@
 		} else if recoverySnapshotVersion := actx.DeviceConfig().RecoverySnapshotVersion(); recoverySnapshotVersion != "current" && recoverySnapshotVersion != "" && c.InRecovery() {
 			snapshotModule = actx.AddVariationDependencies(nil, nil, "recovery_snapshot")
 		}
-		if len(snapshotModule) > 0 {
+		if len(snapshotModule) > 0 && snapshotModule[0] != nil {
 			snapshot := actx.OtherModuleProvider(snapshotModule[0], SnapshotInfoProvider).(SnapshotInfo)
 			*snapshotInfo = &snapshot
 			// republish the snapshot for use in later mutators on this module
 			actx.SetProvider(SnapshotInfoProvider, snapshot)
-		} else {
-			*snapshotInfo = &SnapshotInfo{}
 		}
 	}
-
+	if *snapshotInfo == nil {
+		*snapshotInfo = &SnapshotInfo{}
+	}
 	return **snapshotInfo
 }