ultrahdr: asan fix, default initialize member variable

The default value of mExifPos is commented as -1, but this is missing.
Further size_t is usually defined as unsigned int resulting negative
values as overflow. Best to declare it as ssize_t

Bug: 299596513
Test: atest ultrahdr_unit_test

Change-Id: I187f21aea44914993872def5a4889435d3f2d402
diff --git a/libs/ultrahdr/include/ultrahdr/jpegdecoderhelper.h b/libs/ultrahdr/include/ultrahdr/jpegdecoderhelper.h
index 30149c1..b86ce5f4 100644
--- a/libs/ultrahdr/include/ultrahdr/jpegdecoderhelper.h
+++ b/libs/ultrahdr/include/ultrahdr/jpegdecoderhelper.h
@@ -136,7 +136,7 @@
     size_t mHeight;
 
     // Position of EXIF package, default value is -1 which means no EXIF package appears.
-    size_t mExifPos;
+    ssize_t mExifPos = -1;
 };
 } /* namespace android::ultrahdr  */
 
diff --git a/libs/ultrahdr/jpegr.cpp b/libs/ultrahdr/jpegr.cpp
index 74760d9..705a121 100644
--- a/libs/ultrahdr/jpegr.cpp
+++ b/libs/ultrahdr/jpegr.cpp
@@ -1268,7 +1268,7 @@
   jpegr_compressed_struct new_jpg_image;
   new_jpg_image.data = nullptr;
   new_jpg_image.length = 0;
-  if (decoder.getEXIFPos() != 0) {
+  if (decoder.getEXIFPos() >= 0) {
     if (pExif != nullptr) {
       ALOGE("received EXIF from outside while the primary image already contains EXIF");
       return ERROR_JPEGR_INVALID_INPUT_TYPE;