OpenGL: Fix erroneous handling of BGRX

BGRX was being treated as "BGR input" with "RGBA storage", where it
should have been "BGRA input" with "RGB storage".  So the input for the
texture was expecting 24 bits of packed BGR rather than 32bit BGRX
pixels, and was internally storing it with alpha available.

libobs-opengl/gl-subsystem.h

@@ -42,7 +42,7 @@ static inline GLint convert_gs_format(enum gs_color_format format)
 	case GS_A8:          return GL_RGBA;
 	case GS_R8:          return GL_RED;
 	case GS_RGBA:        return GL_RGBA;
-	case GS_BGRX:        return GL_BGR;
+	case GS_BGRX:        return GL_BGRA;
 	case GS_BGRA:        return GL_BGRA;
 	case GS_R10G10B10A2: return GL_RGBA;
 	case GS_RGBA16:      return GL_RGBA;
@@ -68,7 +68,7 @@ static inline GLint convert_gs_internal_format(enum gs_color_format format)
 	case GS_A8:          return GL_R8; /* NOTE: use GL_TEXTURE_SWIZZLE_x */
 	case GS_R8:          return GL_R8;
 	case GS_RGBA:        return GL_RGBA;
-	case GS_BGRX:        return GL_RGBA;
+	case GS_BGRX:        return GL_RGB;
 	case GS_BGRA:        return GL_RGBA;
 	case GS_R10G10B10A2: return GL_RGB10_A2;
 	case GS_RGBA16:      return GL_RGBA16;