Does not allow an empty MA

[diegomrsantos]

MutliAddress spec doesn't allow an empty address.

Human-readable multiaddr: (/<protoName string>/<value string>)+
Example: /ip4/127.0.0.1/udp/1234
Machine-readable multiaddr: (<protoCode uvarint><value []byte>)+
Same example: 0x4 0x7f 0x0 0x0 0x1 0x91 0x2 0x4 0xd2
Values are usually length-prefixed with a uvarint

[codecov]

Codecov Report

Merging #877 (13c7975) into unstable (4aa615c) will increase coverage by 0.07%.
The diff coverage is 100.00%.

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable     #877      +/-   ##
============================================
+ Coverage     84.16%   84.23%   +0.07%     
============================================
  Files            87       87              
  Lines         15109    15119      +10     
============================================
+ Hits          12717    12736      +19     
+ Misses         2392     2383       -9     

Impacted Files	Coverage Δ
libp2p/stream/chronosstream.nim	76.28% <ø> (ø)
libp2p/multiaddress.nim	86.40% <100.00%> (+0.90%)	⬆️

... and 5 files with indirect coverage changes

[Menduist]

Just linking discussions here: multiformats/rust-multiaddr#85