Check if support for D3DX9 is installed

[anewuser]

Hi. When someone tries to run puNES (D3D9) on a clean Windows install without installing the required DirectX End-User Runtime first, he/she gets an error message saying something like d3dx9_43.dll is missing from your computer:

To make things easier and safer for everyone, can you make puNES check if the runtime is already installed, and then link to https://www.microsoft.com/download/details.aspx?id=35 if it is not? I'm thinking of something like this .NET dialog box:

[punesemu]

To make things easier and safer for everyone, can you make puNES check if the runtime is already installed, and then link to https://www.microsoft.com/download/details.aspx?id=35 if it is not?

Now, if they are not installed, the error message contains the clickable link to the Microsoft page to download them.

[anewuser]

@punesemu Thank you. I was also going to create a separate issue about recommending the DXD9 build if the system doesn't support the minimum required OpenGL version. Currently, it gives this error on my Pentium P6200 laptop:

OpenGL error