Allow less-loader to use webpack resolver when no includePaths are given

[vincentjames501]

• If you look at https://github.com/webpack-contrib/less-loader#less-resolver, it states that
  if you provide paths, it will use the less resolver. We should only use the less-resolver when
  stylePreprocessorOptions.includePaths are actually given.
• This fixes issues where if in your less file you @import "~@dependency/less-file"; it actually
  resolves correct and when you import something like @import "some-local-file"; it actually
  recompiles when ng build --watch is ran.

[clydin]

That was the original intent of the otherwise unnecessary lessPathOptions variable. Somewhere along the way someone changed it to include an empty array by default. This is indeed a defect. Thank you for the fix.

[clydin]

Note also that the commit message should start with fix(@angular-devkit/build-angular):

[vincentjames501]

@clydin fixed the commit message. Thanks.

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