fix: Restore STDERR in pngtest.c

In "test: Add consistency checks for the PNG_LIBPNG_VER* number" [0] the
`STDERR` macro was moved from outside an `ifdef` to inside an `ifdef`.
This broke the code in the `else` of this `ifdef` which also uses the
`STDERR` macro. Move `STDERR` back to where it was to avoid compile
errors in the `else` case.

[0] cc8006c

Fixes: #560
Reviewed-by: Cosmin Truta <[email protected]>
Signed-off-by: Cosmin Truta <[email protected]>

pngtest.c

@@ -45,6 +45,11 @@
 
 #include "png.h"
 
+/* This hack was introduced for historical reasons, and we are
+ * still keeping it in libpng-1.6.x for compatibility reasons.
+ */
+#define STDERR stdout
+
 /* Generate a compiler error if there is an old png.h in the search path. */
 typedef png_libpng_version_1_6_44_git Your_png_h_is_not_version_1_6_44_git;
 
@@ -103,11 +108,6 @@ typedef png_libpng_version_1_6_44_git Your_png_h_is_not_version_1_6_44_git;
 typedef FILE * png_FILE_p;
 #endif
 
-/* This hack was introduced for historical reasons, and we are
- * still keeping it in libpng-1.6.x for compatibility reasons.
- */
-#define STDERR stdout
-
 #ifndef PNG_DEBUG
 #  define PNG_DEBUG 0
 #endif