For nonuniformEXT constructor, make a copy of the node to decorate

Test/spv.nonuniform2.frag

@@ -0,0 +1,9 @@
+#version 450
+#extension GL_EXT_nonuniform_qualifier : require
+layout(set=0,binding=4,rgba32f) uniform imageBuffer data[];
+layout(location = 0) out vec4     FragColor;
+layout(location = 3) in flat int  rIndex;
+void main()
+{
+  FragColor = imageLoad(data[nonuniformEXT(rIndex)], 0);
+}