Combine imports/import files earlier

If we wait until after adjusting the paths relative to the new
target, we may fail to import them because the path they'll be
relative to may not yet exist.

If we do it after moving path

src/CSS.php

@@ -314,22 +314,20 @@ public function execute($path = null)
             // restore the string we've extracted earlier
             $css = $this->restoreExtractedData($css);
 
+            $source = $source ?: '';
+            $css = $this->combineImports($source, $css);
+            $css = $this->importFiles($source, $css);
+
             /*
              * If we'll save to a new path, we'll have to fix the relative paths
              * to be relative no longer to the source file, but to the new path.
              * If we don't write to a file, fall back to same path so no
              * conversion happens (because we still want it to go through most
              * of the move code...)
              */
-            $source = $source ?: '';
             $converter = new Converter($source, $path ?: $source);
             $css = $this->move($converter, $css);
 
-            // if no target path is given, relative paths were not converted, so
-            // they'll still be relative to the source file then
-            $css = $this->importFiles($path ?: $source, $css);
-            $css = $this->combineImports($path ?: $source, $css);
-
             // combine css
             $content .= $css;
         }