Invalid media query merge of MQs inside @import with MQ

Tested with 1.4.2 RELEASE and 1.5.0-wip 6fe11743828addd1c7d7bcf320364cc28dc21d8d

A media query in a LESS file imported using import with a media query results in an invalid query.

import-test-f.less

@media screen and (min-device-pixel-ratio: 2) {
  #css {
    color: purple;
  }
}

import.less

@import "import/import-test-f" screen and (max-width: 604px);

The expected output is

@media screen and (max-width: 604px) and (min-device-pixel-ratio: 2) {
  #css {
    color: purple;
  }
}

but instead we have

@media screen and (max-width: 604px) and screen and (min-device-pixel-ratio: 2) {
  #css {
    color: purple;
  }
}

which is an invalid media query. [http://www.w3.org/TR/css3-mediaqueries/#syntax]

Furthermore, in 1.4.2 we have an empty media query with just max-width. This is no longer appearing in the 1.5.0-wip commit above.

Coincidently, the original test fails in 1.4.2 despite the fact that bin/lessc itself outputs the expected CSS. This seems to have been corrected in 1.5.0-wip as well.

Reproduce the issue with _import-test-f.less and _import.less, comparing the generated media query with the expected output. Start by locating the original test referenced in the report and the Less import/media-query handling it exercises. Done means the nested queries merge without the duplicated screen term and the existing test passes across the affected versions.