win-capture: Use PSAPI GetProcessImageFileName

If the PSAPI_VERSION macro is not set to 1 when using
GetProcessImageFileName, it will attempt to import it as
K32GetProcessImageFileName from kernel32.dll instead of psapi.dll, which
breaks compatibility with vista and xp.

plugins/win-capture/window-helpers.c

@@ -1,3 +1,4 @@
+#define PSAPI_VERSION 1
 #include <obs.h>
 #include <util/dstr.h>