Transcoding: Change to use string path instead of fd.

Bug: 145628554
Test: unit test

Change-Id: I321ecf75e770b4500fc3015a5d161e3b48ea5678
diff --git a/media/libmediatranscoding/TranscodingClientManager.cpp b/media/libmediatranscoding/TranscodingClientManager.cpp
index de9dd76..ce3ac13 100644
--- a/media/libmediatranscoding/TranscodingClientManager.cpp
+++ b/media/libmediatranscoding/TranscodingClientManager.cpp
@@ -112,7 +112,7 @@
         return Status::fromServiceSpecificError(IMediaTranscodingService::ERROR_DISCONNECTED);
     }
 
-    if (in_request.fileName.empty()) {
+    if (in_request.sourceFilePath.empty() || in_request.destinationFilePath.empty()) {
         // This is the only error we check for now.
         return Status::ok();
     }