Ftp client: Fix burst download (#2235) #3741

Job	Run time
coverage (ubuntu-20.04)	4m 59s
ubuntu-20.04 (package, non-mavsdk_server)	6m 34s
Ubuntu/Debian packaging (Ubuntu 20.04)	6m 2s
alpine 3.19.0 (musl)	9m 34s
ubuntu-22.04 (package, non-mavsdk_server)	5m 20s
android-arm	5m 24s
linux-armv6	5m 3s
android-arm64	5m 29s
linux-armv6-musl	10m 6s
linux-armv7	5m 0s
ios	6m 44s
linux-armv7l-musl	9m 53s
android-x86	5m 15s
linux-arm64	4m 59s
ios_simulator	8m 17s
android-x86_64	5m 16s
linux-arm64-musl	10m 37s
macOS	11m 28s
ubuntu-20.04 (non-mavsdk_server, non-superbuild)	5m 17s
ubuntu-20.04 (mavsdk, hunter)	4m 0s
macOS-framework	15m 12s
ubuntu-22.04 (style and proto check)	1m 32s
ubuntu-20.04 (mavsdk_server, superbuild)	12m 14s
Windows	12m 1s
ubuntu-22.04 (mavsdk_server, superbuild)	10m 30s
iOS XCFramework	53s
	3h 7m 39s

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