GPU: Texture bit should be ignored when drawing lines

Fixes line flickering in Vagrant Story.

src/core/gpu.h

@@ -208,7 +208,10 @@ protected:
     BitField<u32, bool, 28, 1> shading_enable;              // 0 - flat, 1 = gouroud
     BitField<u32, Primitive, 29, 21> primitive;
 
-    // Returns true if dithering should be enabled. Depends on the primitive type.
+    /// Returns true if texturing should be enabled. Depends on the primitive type.
+    bool IsTexturingEnabled() const { return (primitive != Primitive::Line) ? texture_enable : false; }
+
+    /// Returns true if dithering should be enabled. Depends on the primitive type.
     bool IsDitheringEnabled() const
     {
       switch (primitive)

src/core/gpu_hw.cpp

@@ -274,7 +274,7 @@ void GPU_HW::CopyVRAM(u32 src_x, u32 src_y, u32 dst_x, u32 dst_y, u32 width, u32
 void GPU_HW::DispatchRenderCommand(RenderCommand rc, u32 num_vertices, const u32* command_ptr)
 {
   TextureMode texture_mode;
-  if (rc.texture_enable)
+  if (rc.IsTexturingEnabled())
   {
     // texture page changed - check that the new page doesn't intersect the drawing area
     if (m_draw_mode.IsTexturePageChanged())