Failed to load proto files from external domains

[ridomin]

protobuf.js version: 7.1.2

When loading proto files from external domains, the URL gets normalized with protobufjs/path missing one slash

 root = await protobuf.load("https://mydomain/path/file.proto")

I've observed this call

protobuf.js/src/root.js

Line 205 in d026849

if (resolved = self.resolvePath("", filename[i]))

translates the URL into https:/mydomain/path/file.proto

I've submitted this PR to do not normalize http[s] paths
#1820