rsx: Default initialize vertex program fields

- Fixes a crash when RSXVertexProgram is default-initialized. This
  probably also fixes a whole class of crashes that occur when
  shader interpreter is in use since that pipeline uses a
  default-initialized stub.

rpcs3/Emu/RSX/Program/RSXVertexProgram.h

@@ -223,10 +223,10 @@ struct RSXVertexProgram
 {
 	std::vector<u32> data;
 	rsx::vertex_program_texture_state texture_state;
-	u32 ctrl;
+	u32 ctrl = 0;
-	u32 output_mask;
+	u32 output_mask = 0;
-	u32 base_address;
+	u32 base_address = 0;
-	u32 entry;
+	u32 entry = 0;
 	std::bitset<rsx::max_vertex_program_instructions> instruction_mask;
 	std::set<u32> jump_table;