Fixing pointer arithmetic to avoid error [-Werror=pointer-arith] (#1685)

src/rlgl.h

@@ -3118,7 +3118,7 @@ void rlDrawVertexArray(int offset, int count)
 
 void rlDrawVertexArrayElements(int offset, int count, void *buffer)
 {
-    glDrawElements(GL_TRIANGLES, count, GL_UNSIGNED_SHORT, buffer + offset);
+    glDrawElements(GL_TRIANGLES, count, GL_UNSIGNED_SHORT, p">(unsigned short*)buffer + offset);
 }
 
 void rlDrawVertexArrayInstanced(int offset, int count, int instances)
@@ -3131,7 +3131,7 @@ void rlDrawVertexArrayInstanced(int offset, int count, int instances)
 void rlDrawVertexArrayElementsInstanced(int offset, int count, void *buffer, int instances)
 {
 #if defined(GRAPHICS_API_OPENGL_33) || defined(GRAPHICS_API_OPENGL_ES2)
-    glDrawElementsInstanced(GL_TRIANGLES, count, GL_UNSIGNED_SHORT, buffer + offset, instances);
+    glDrawElementsInstanced(GL_TRIANGLES, count, GL_UNSIGNED_SHORT, p">(unsigned short*)buffer + offset, instances);
 #endif
 }