Fix crash when old Android Studio (<2.2.0) is installed (#9009)

Old Android Stuio versions pior to 2.2.0 didn't come with Java bundled. Make sure flutter doesn't crash when we try to determine the Java version of those old Android Studio installations.

packages/flutter_tools/lib/src/android/android_studio.dart

@@ -282,14 +282,19 @@ class AndroidStudio implements Comparable<AndroidStudio> {
     final String javaPath = platform.isMacOS ?
         fs.path.join(directory, 'jre', 'jdk', 'Contents', 'Home') :
         fs.path.join(directory, 'jre');
-    final ProcessResult result = processManager.runSync(<String>[fs.path.join(javaPath, 'bin', 'java'), '-version']);
-    if (result.exitCode == 0) {
-      final List<String> versionLines = result.stderr.split('\n');
-      final String javaVersion = versionLines.length >= 2 ? versionLines[1] : versionLines[0];
-      _validationMessages.add('Java version: $javaVersion');
-      _javaPath = javaPath;
-    } else {
+    final String javaExecutable = fs.path.join(javaPath, 'bin', 'java');
+    if (!processManager.canRun(javaExecutable)) {
       _validationMessages.add('Unable to find bundled Java version.');
+    } else {
+      final ProcessResult result = processManager.runSync(<String>[javaExecutable, '-version']);
+      if (result.exitCode == 0) {
+        final List<String> versionLines = result.stderr.split('\n');
+        final String javaVersion = versionLines.length >= 2 ? versionLines[1] : versionLines[0];
+        _validationMessages.add('Java version: $javaVersion');
+        _javaPath = javaPath;
+      } else {
+        _validationMessages.add('Unable to determine bundled Java version.');
+      }
     }
   }