Fix empty line handling in line directive callback.

The current line number for the #line directive should be passed
in as parameter to the line directive callback. Without it, we
don't know how many empty lines we should output.

Test/baseResults/preprocessor.line.vert.out

@@ -1,23 +1,39 @@
-#line 300
-
-#line 2
-
-#line 10
-
-#line 2
-
-#line 0
-#line 4
-
-#line 8
-
-void main(){
-  gl_Position = vec4(10);
-}
-#line 8 4
-
-#line 12 3
-
-#line 1
-
-
+#line 300
+
+#line 2
+
+
+
+
+
+#line 10
+
+
+#line 2
+
+#line 0
+
+
+
+#line 4
+
+
+
+
+
+#line 8
+
+void main(){
+  gl_Position = vec4(10);
+}
+
+#line 8 4
+
+
+
+
+#line 12 3
+
+#line 1
+
+