fix for mp4 with only one GPMF payload

demo/GPMF_mp4reader.c

@@ -850,7 +850,7 @@ size_t OpenMP4Source(char *filename, uint32_t traktype, uint32_t traksubtype)  /
 
 									totaldur += duration;
 									mp4->metadatalength += (double)((double)samplecount * (double)duration / (double)mp4->meta_clockdemon);
-									if (samplecount > 1 || entries == 0)
+									if (samplecount > 1 || num == 1)
 										mp4->basemetadataduration = mp4->metadatalength * (double)mp4->meta_clockdemon / (double)samples;
 								}
 							}