Docs generation breaks with custom module name generation when using typedoc v0.19.2

[anmolarora1]

The typedoc generation fails with v0.19.2 when a custom module name generation mapper is used because it's assumed that the rootFileNames would always be a non-empty array.

typedoc-plugin-external-module-name/typedoc-plugin-external-module-name.ts

Line 103 in 5af43c4

path.resolve(rootFileNames[0]),

There's no such expectation in the method definition in though - check getRootFileNames method (taken from Typescript)

As a result, the function breaks unexpectedly when there are no rootFileNames

The solution might be fiddlier than it seems, but adding an empty array check on this line prevents unexpected errors for now.

[christopherthielen]

The root path auto-detection code assumed you used files in your tsconfig.json and didn't account for includes syntax.
This fix should fall back to using the current directory instead when includes is used.

Released in version 4.0.4

@anmolarora1