better error when file does not exist

[teto]

there should be a better error than

�[m�[91mexamples/client_2_filtered.pcapng> �[39mmap-tcp examples/client_2_filtered.pcapng examples/server_2_filtered 0
...
�[m�[32m[debug]�[39m [M.Loader#82] cache miss: "Not implemented yet"
�[m�[32m[debug]�[39m [M.Loader#83] Calling tshark
�[mExporting fields ["frame.time_epoch","frame.interface_name","_ws.col.ipdst","ip.dst_host","_ws.col.ipsrc","ip.src_host","mptcp.ack","tcp.options.mptcp.datafin.flag","mptcp.dsn","mptcp.expected_token","tcp.options.mptcp.recvkey","tcp.options.mptcp.recvtok","tcp.options.mptcp.sendkey","mptcp.stream","tcp.options.mptcp.ve
�[mrsion","frame.number","mptcp.reinjection_of","mptcp.reinjection_of","frame.time_relative","mptcp.related_mapping","tcp.window_size","tcp.ack","tcp.dstport","tcp.flags","tcp.len","tcp.option_kind","tcp.seq","tcp.srcport","tcp.stream","tcp.options.timestamp.tsecr","tcp.options.timestamp.tsval"]
�[mCommand run: RawCommand "tshark" ["-E","separator=|","-r","examples/server_2_filtered","-o","mptcp.analyze_mptcp:true","-o","mptcp.intersubflows_retransmission:true","-o","mptcp.relative_sequence_numbers:true","-o","mptcp.analyze_mappings:true","-o","tcp.analyze_sequence_numbers:true","-o","gui.column.format:Time,%At,i
�[mpsrc,%s,ipdst,%d","-2","-R","mptcp or tcp and not icmp","-T","fields","-e","frame.time_epoch","-e","frame.interface_name","-e","_ws.col.ipdst","-e","ip.dst_host","-e","_ws.col.ipsrc","-e","ip.src_host","-e","mptcp.ack","-e","tcp.options.mptcp.datafin.flag","-e","mptcp.dsn","-e","mptcp.expected_token","-e","tcp.options.
�[mmptcp.recvkey","-e","tcp.options.mptcp.recvtok","-e","tcp.options.mptcp.sendkey","-e","mptcp.stream","-e","tcp.options.mptcp.version","-e","frame.number","-e","mptcp.reinjection_of","-e","mptcp.reinjection_of","-e","frame.time_relative","-e","mptcp.related_mapping","-e","tcp.window_size","-e","tcp.ack","-e","tcp.dstpor
�[mt","-e","tcp.flags","-e","tcp.len","-e","tcp.option_kind","-e","tcp.seq","-e","tcp.srcport","-e","tcp.stream","-e","tcp.options.timestamp.tsecr","-e","tcp.options.timestamp.tsval"]
�[m�[34m[info] �[39m [M.Loader#102] Error happened: ExitFailure 2
�[mmptcpanalyzer: fd:6: hGetContents: illegal operation (delayed read on closed handle)

when a file does not exist