OpenGL2: Fix OpenArena speed powerup drawing solid black

OpenArena's speed powerup model uses rgbGen vertex but MD3 models don't
provide a vertex color. The opengl1 renderer uses whatever previous
vertex color was set (and changed based on surface draw order).

There isn't a simple way to emulate that in the OpenGL2 renderer so use
white vertex color.

Author: zturtleman

code/renderercommon/qgl.h

@@ -188,6 +188,7 @@ extern void (APIENTRYP qglUnlockArraysEXT) (void);
 	GLE(void, UniformMatrix4fv, GLint location, GLsizei count, GLboolean transpose, const GLfloat *value) \
 	GLE(void, ValidateProgram, GLuint program) \
 	GLE(void, VertexAttribPointer, GLuint index, GLint size, GLenum type, GLboolean normalized, GLsizei stride, const void *pointer) \
+	GLE(void, VertexAttrib4fv, GLuint index, const GLfloat *values) \
 
 // GL_NVX_gpu_memory_info
 #ifndef GL_NVX_gpu_memory_info

code/renderergl2/tr_vbo.c

@@ -90,6 +90,12 @@ void Vao_SetVertexPointers(vao_t *vao)
 
 			if (!glRefConfig.vertexArrayObject || vao == tess.vao)
 				glState.vertexAttribsEnabled &= ~attribBit;
+
+			// set vertex color to white for models without vertex colors
+			if (attribIndex == ATTR_INDEX_COLOR) {
+				float white[4] = { 1, 1, 1, 1 };
+				qglVertexAttrib4fv(attribIndex, white);
+			}
 		}
 	}
 }