Migrate from android::String isEmpty to empty [bootanimation]

This empty method is different from the old one - it aligns with
std::string definition.

Bug: 295394788
Test: make checkbuild
Change-Id: Ib80c839df7ff7e3fb0ed2df7a00393d843d44d9d
diff --git a/cmds/bootanimation/BootAnimation.cpp b/cmds/bootanimation/BootAnimation.cpp
index 8ceb9ec..74ca41d 100644
--- a/cmds/bootanimation/BootAnimation.cpp
+++ b/cmds/bootanimation/BootAnimation.cpp
@@ -691,7 +691,7 @@
 
 bool BootAnimation::preloadAnimation() {
     findBootAnimationFile();
-    if (!mZipFileName.isEmpty()) {
+    if (!mZipFileName.empty()) {
         mAnimation = loadAnimation(mZipFileName);
         return (mAnimation != nullptr);
     }
@@ -821,7 +821,7 @@
 
     // We have no bootanimation file, so we use the stock android logo
     // animation.
-    if (mZipFileName.isEmpty()) {
+    if (mZipFileName.empty()) {
         ALOGD("No animation file");
         result = android();
     } else {