fixing load_png() so it checks the correct pointer

encoder/basisu_enc.cpp

diff --git a/encoder/basisu_enc.cpp b/encoder/basisu_enc.cpp
index 47e8981..0636d71 100644
--- a/encoder/basisu_enc.cpp
+++ b/encoder/basisu_enc.cpp
@@ -430,7 +430,7 @@
 
 		uint32_t width = 0, height = 0, num_chans = 0;
 		void* pImage = pv_png::load_png(pBuf, buf_size, 4, width, height, num_chans);
-		if (!pBuf)
+		if (!pImage)
 		{
 			error_printf("pv_png::load_png failed while loading image \"%s\"\n", pFilename);
 			return false;