ExifInterface: Prevent DATETIME value from being set unproperly

Although the DATETIME and DATETIME_ORIGINAL tags are for different
purposes, the DATETIME value is set to the same value as
DATETIME_ORIGINAL tag's when loading the attributes of an image.
This CL prevents the problem by setting the value of DATETIME tag only
when it does not exist.

Bug: 62137632
Test: Passed ExifInterface CTS
Change-Id: Ic5c43c53cb363a782bcac20915d74ea534ec70e4

media/java/android/media/ExifInterface.java

@@ -2661,9 +2661,9 @@ public class ExifInterface {
     }
 
     private void addDefaultValuesForCompatibility() {
-        // The value of DATETIME tag has the same value of DATETIME_ORIGINAL tag.
+        // If DATETIME tag has no value, then set the value to DATETIME_ORIGINAL tag's.
         String valueOfDateTimeOriginal = getAttribute(TAG_DATETIME_ORIGINAL);
-        if (valueOfDateTimeOriginal != null) {
+        if (valueOfDateTimeOriginal != null && getAttribute(TAG_DATETIME) == null) {
             mAttributes[IFD_TYPE_PRIMARY].put(TAG_DATETIME,
                     ExifAttribute.createString(valueOfDateTimeOriginal));
         }