Fetch parameters if they are |Ref|s in Pattern color spaces (issue 6081)

Fixes 6081.

src/core/colorspace.js

@@ -260,7 +260,7 @@ var ColorSpace = (function ColorSpaceClosure() {
           error('unrecognized colorspace ' + mode);
       }
     } else if (isArray(cs)) {
-      mode = cs[0].name;
+      mode = xref.fetchIfRef(cs[0]).name;
       this.mode = mode;
       var numComps, params;
 
@@ -293,7 +293,7 @@ var ColorSpace = (function ColorSpaceClosure() {
           }
           break;
         case 'Pattern':
-          var basePatternCS = cs[1];
+          var basePatternCS = xref.fetchIfRef(cs[1]) || null;
           if (basePatternCS) {
             basePatternCS = ColorSpace.parseToIR(basePatternCS, xref, res);
           }

test/pdfs/.gitignore

@@ -134,3 +134,4 @@
 !issue5909.pdf
 !issue6010_1.pdf
 !issue6010_2.pdf
+!issue6081.pdf

test/test_manifest.json

@@ -1531,6 +1531,13 @@
       "type": "eq",
       "about": "Pattern with current transform different than base transform."
     },
+    {  "id": "issue6081",
+       "file": "pdfs/issue6081.pdf",
+       "md5": "854326ce9178d10ff4a0ff2aedf67e45",
+       "rounds": 1,
+       "link": false,
+       "type": "eq"
+    },
     {  "id": "issue2462",
       "file": "pdfs/issue2462.pdf",
       "md5": "d4e3dddfdd35464c71cf0310bff29b42",