Fix integer underflow in ESDS processing

Several arithmetic operations within parseESDescriptor could underflow, leading
to an out-of-bounds read operation. Ensure that subtractions from 'size' do not
cause it to wrap around.

Bug: 20139950
Change-Id: I0d1b136ce68fd7c6f606ce66714bf644cfb2961c
(cherry picked from commit 07c0f59d6c48874982d2b5c713487612e5af465a)
diff --git a/media/libstagefright/ESDS.cpp b/media/libstagefright/ESDS.cpp
index 4a0c35c..c76bc4a 100644
--- a/media/libstagefright/ESDS.cpp
+++ b/media/libstagefright/ESDS.cpp
@@ -136,6 +136,8 @@
     --size;
 
     if (streamDependenceFlag) {
+        if (size < 2)
+            return ERROR_MALFORMED;
         offset += 2;
         size -= 2;
     }
@@ -145,11 +147,15 @@
             return ERROR_MALFORMED;
         }
         unsigned URLlength = mData[offset];
+        if (URLlength >= size)
+            return ERROR_MALFORMED;
         offset += URLlength + 1;
         size -= URLlength + 1;
     }
 
     if (OCRstreamFlag) {
+        if (size < 2)
+            return ERROR_MALFORMED;
         offset += 2;
         size -= 2;