fix premature conversion of casts containing dimension queries

test/basic/package_function_cast.v

@@ -0,0 +1,18 @@
+module top;
+    function automatic [7:0] f;
+        input [2:0] p;
+        begin
+            f = 7'b0;
+            f[p+:2] = 2'b11;
+        end
+    endfunction
+    reg [2:0] p;
+    wire [7:0] q;
+    assign q = f(p);
+    initial begin
+        $monitor("%0d, p=%b q=%b", $time, p, q);
+        #1 p = 0;
+        while (p != 7)
+            #1 p = p + 1;
+    end
+endmodule