HLSL: allow trailing commas in initializer lists & scalar initialization

Test/hlsl.init2.frag

@@ -3,20 +3,29 @@ void Test1()
 {
     struct mystruct { float2 a; };
     mystruct test1 = {
-        { 1, 2, },          // test trailing commas
+        { 1, 2, },          // test trailing commas in list
     };
 
     mystruct test2 = {
-        { { 1, 2, } },      // test unneeded levels
+        float2(3, 4),
     };
 
-    float test3 = { 1 } ;   // test scalar initialization
+    // mystruct test3 = {
+    //     { { 5, 6, } },   // TODO: test unneeded levels
+    // };
+
+    float test4 = { 7, } ;   // test scalar initialization
+
+    struct mystruct2 { float a; float b; float c; };
+    mystruct2 test5 = { {8,}, {9,}, {10}, };
 }
 
 struct PS_OUTPUT { float4 color : SV_Target0; };
 
 PS_OUTPUT main()
 {
+    Test1();
+
     PS_OUTPUT ps_output;
     ps_output.color = 1.0;
     return ps_output;