Fix: MediaPlaylist with discontinuities should not ignore maps

[vish91]

MediaPlaylist with discontinuities should not ignore segment maps
https://tools.ietf.org/html/draft-pantos-http-live-streaming-23#section-4.3.2.5
https://developer.apple.com/documentation/http_live_streaming/hls_authoring_specification_for_apple_devices 8.20

MediaPlaylist with default Map and discontinuities should always have segment Maps, referring to the media initialization section after it ( be it content or ads or even if it is same as the DefaultMap )

Example:
today we get

#EXT-X-VERSION:5
#EXT-X-MAP:URI="https://example.com/content-init.mp4",BYTERANGE=1024000@1048576
#EXT-X-MEDIA-SEQUENCE:0
#EXT-X-TARGETDURATION:6
#EXTINF:5.000,
test01.mp4
#EXT-X-DISCONTINUITY
#EXTINF:6.000,
test02.mp4
#EXTINF:6.000,
test03.mp4
#EXT-X-DISCONTINUITY
#EXTINF:6.000,
test04.mp4
#EXTINF:6.000,
test05.mp4

instead we should expect:

#EXT-X-VERSION:5
#EXT-X-MAP:URI="https://example.com/content-init.mp4",BYTERANGE=1024000@1048576
#EXT-X-MEDIA-SEQUENCE:0
#EXT-X-TARGETDURATION:6
#EXTINF:5.000,
test01.mp4
#EXT-X-DISCONTINUITY
#EXT-X-MAP:URI="https://segmentencoded.com/ad-init.mp4",BYTERANGE=1024000@1048576
#EXTINF:6.000,
test02.mp4
#EXTINF:6.000,
test03.mp4
#EXT-X-DISCONTINUITY
#EXT-X-MAP:URI="https://example.com/content-init.mp4",BYTERANGE=1024000@1048576
#EXTINF:6.000,
test04.mp4
#EXTINF:6.000,
test05.mp4

[coveralls]

Coverage increased (+0.2%) to 75.58% when pulling 08b2d91 on zencoder:master into 2ce07e6 on grafov:master.

[coveralls]

Coverage increased (+0.2%) to 75.58% when pulling 08b2d91 on zencoder:master into 2ce07e6 on grafov:master.

[coveralls]

Coverage increased (+0.2%) to 75.58% when pulling 08b2d91 on zencoder:master into 2ce07e6 on grafov:master.

[vish91]

@grafov or @leikao would appreciate if someone can review and merge this please