[libpng16] Revert change to png_malloc_array(). It's not needed

now that iCCP profile_length honors PNG_USER_CHUNK_MALLOC_MAX.

ANNOUNCE

@@ -26,8 +26,6 @@ Other information:
 Changes since the last public release (1.6.24):
 
 Version 1.6.25beta01 [August 11, 2016]
-  Return NULL from png_malloc_array() with a warning instead of calling
-    png_error() on failure.
   Reject oversized iCCP profile immediately.
   Cleaned up PNG_DEBUG compile of pngtest.c.
 

CHANGES

@@ -5676,8 +5676,6 @@ Version 1.6.24[August 4, 2016]
   No changes.
 
 Version 1.6.25beta01 [August 11, 2016]
-  Return NULL from png_malloc_array() with a warning instead of calling
-    png_error() on failure.
   Reject oversized iCCP profile immediately.
   Cleaned up PNG_DEBUG compile of pngtest.c.
 

pngmem.c

 
 /* pngmem.c - stub functions for memory allocation
  *
- * Last changed in libpng 1.6.25 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.24 [August 4, 2016]
  * Copyright (c) 1998-2002,2004,2006-2014,2016 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
@@ -123,10 +123,7 @@ png_malloc_array,(png_const_structrp png_ptr, int nelements,
     size_t element_size),PNG_ALLOCATED)
 {
    if (nelements <= 0 || element_size == 0)
-   {
-      png_warning(png_ptr, "internal error: array alloc");
-      return NULL;
-   }
+      png_error(png_ptr, "internal error: array alloc");
 
    return png_malloc_array_checked(png_ptr, nelements, element_size);
 }