[libpng16] Fixed unused "wrote_question" in non-write pngtest.

pngtest.c

@@ -115,7 +115,9 @@ static int relaxed = 0;
 static int unsupported_chunks = 0; /* chunk unsupported by libpng in input */
 static int error_count = 0; /* count calls to png_error */
 static int warning_count = 0; /* count calls to png_warning */
+#ifdef PNG_WRITE_SUPPORTED
 static int wrote_question = 0;
+#endif
 
 #ifdef __TURBOC__
 #include <mem.h>
@@ -1581,13 +1583,11 @@ test_one_file(PNG_CONST char *inname, PNG_CONST char *outname)
 
 #ifdef PNG_WRITE_SUPPORTED /* else nothing was written */
    {
-
       for (;;)
       {
          png_size_t num_in, num_out;
          char inbuf[256], outbuf[256];
 
-
          num_in = fread(inbuf, 1, sizeof inbuf, fpin);
          num_out = fread(outbuf, 1, sizeof outbuf, fpout);