Migrate from android::String isEmpty to empty

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

Bug: 295394788
Test: make checkbuild
Change-Id: I890b3dfa930002f4406e9d9aec024f94ada1cad0
diff --git a/services/audioflinger/PatchPanel.cpp b/services/audioflinger/PatchPanel.cpp
index 972c870..351c618 100644
--- a/services/audioflinger/PatchPanel.cpp
+++ b/services/audioflinger/PatchPanel.cpp
@@ -928,7 +928,7 @@
         }
     }
 
-    if (!patchPanelDump.isEmpty()) {
+    if (!patchPanelDump.empty()) {
         write(fd, patchPanelDump.c_str(), patchPanelDump.size());
     }
 }