wrlib: initialise value for variable to avoid possible crash (Coverity #50245)

As pointed by Coverity, there's a free on the content of this buffer at
function's end, but if the image's width or height is lower than 1 then we
could reach this free before allocating anything, thus having an
uninitialised pointer.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>

wrlib/load_jpeg.c

@@ -132,6 +132,7 @@ RImage *RLoadJPEG(const char *file_name)
 	jpeg_read_header(&cinfo, TRUE);
 
 	if (cinfo.image_width < 1 || cinfo.image_height < 1) {
+		buffer[0] = NULL;	/* Initialize pointer to avoid spurious free in cleanup code */
 		RErrorCode = RERR_BADIMAGEFILE;
 		goto bye;
 	}