m4a examples: file does not support isOpen()

Author: pschatzmann

tests-cmake/codec/container-m4a/m4a.ino

@@ -33,7 +33,7 @@ void setup() {
   }
 
   file = SD.open("/home/pschatzmann/Music/m4a/alac.m4a");
-  if (!file.isOpen()) {
+  if (!file) {
     Serial.println("Failed to open file!");
     return;
   }

tests-cmake/codec/m4a-extractor/m4a-extrator.ino

@@ -34,7 +34,7 @@ void setup() {
   }
 
   file = SD.open("/home/pschatzmann/Music/m4a/1-07 All You Need Is Love.m4a");
-  if (!file.isOpen()) {
+  if (!file) {
     Serial.println("Failed to open file!");
     return;
   }