fate: add a more extensive test for APNG_DISPOSE_OP_BACKGROUND

Uses the sample from #9184.

tests/fate/apng.mak

@@ -10,6 +10,9 @@ fate-apng-dispose-previous: CMD = framecrc -i $(TARGET_SAMPLES)/apng/apng_out_of
 FATE_APNG += fate-apng-dispose-background
 fate-apng-dispose-background: CMD = framecrc -i $(TARGET_SAMPLES)/apng/015.png
 
+FATE_APNG += fate-apng-dispose-background2
+fate-apng-dispose-background2: CMD = framecrc -i $(TARGET_SAMPLES)/apng/alogo.png
+
 FATE_APNG-$(call DEMDEC, APNG, APNG) += $(FATE_APNG)
 
 FATE_SAMPLES_FFMPEG += $(FATE_APNG-yes)

tests/ref/fate/apng-dispose-background2

@@ -0,0 +1,25 @@
+#tb 0: 3/40
+#media_type 0: video
+#codec_id 0: rawvideo
+#dimensions 0: 100x100
+#sar 0: 0/1
+0,          0,          0,        1,    40000, 0x15284fcd
+0,          1,          1,        1,    40000, 0xc77f0451
+0,          2,          2,        1,    40000, 0x895c4029
+0,          3,          3,        1,    40000, 0x9474bd69
+0,          4,          4,        1,    40000, 0xdd67407e
+0,          5,          5,        1,    40000, 0x2ff049ee
+0,          6,          6,        1,    40000, 0xd944c1bb
+0,          7,          7,        1,    40000, 0x56850692
+0,          8,          8,        1,    40000, 0x8816ce06
+0,          9,          9,        1,    40000, 0x0d7170a8
+0,         10,         10,        1,    40000, 0x85290373
+0,         11,         11,        1,    40000, 0xd2899862
+0,         12,         12,        1,    40000, 0x8730ed6d
+0,         13,         13,        1,    40000, 0x914257ad
+0,         14,         14,        1,    40000, 0x513b88a4
+0,         15,         15,        1,    40000, 0x695a8ff0
+0,         16,         16,        1,    40000, 0xec63be20
+0,         17,         17,        1,    40000, 0x024a7b99
+0,         18,         18,        1,    40000, 0x28b05fc4
+0,         19,         19,        1,    40000, 0xcf1fceb2