Distinguish jar folders and jar files in ApkBuilder script

Checking if -rj parameter value is a directory or a file
and calling the appropriate function for each of them.
diff --git a/tools/apkbuilder/src/com/android/apkbuilder/internal/ApkBuilderImpl.java b/tools/apkbuilder/src/com/android/apkbuilder/internal/ApkBuilderImpl.java
index 81cbc1c..9d21c22 100644
--- a/tools/apkbuilder/src/com/android/apkbuilder/internal/ApkBuilderImpl.java
+++ b/tools/apkbuilder/src/com/android/apkbuilder/internal/ApkBuilderImpl.java
@@ -133,7 +133,12 @@
                     throw new WrongOptionException("Missing value for -rj");
                 }
 
-                processJarFolder(args[index++], resourcesJars);
+                File f = new File(args[index]);
+                if (f.isDirectory()) {
+                    processJarFolder(args[index++], resourcesJars);
+                } else if (f.isFile()) {
+                    processJarFile(args[index++], resourcesJars);
+                }
             } else if ("-nf".equals(argument)) {
                 // quick check on the next argument.
                 if (index == args.length) {