Make SDL_SetError and friends unconditionally return -1.

This lets us change things like this...

    if (Failed) {
        SDL_SetError("We failed");
        return -1;
    }

...into this...

    if (Failed) {
        return SDL_SetError("We failed");
    }


 Fixes Bugzilla #1778.

src/video/directfb/SDL_DirectFB_opengl.c

@@ -72,8 +72,7 @@ DirectFB_GL_Initialize(_THIS)
                                                sizeof(struct
                                                       SDL_GLDriverData));
     if (!_this->gl_data) {
-        SDL_OutOfMemory();
-        return -1;
+        return SDL_OutOfMemory();
     }
     _this->gl_data->initialized = 0;
 
@@ -115,8 +114,7 @@ DirectFB_GL_LoadLibrary(_THIS, const char *path)
     SDL_DFB_DEBUG("Loadlibrary : %s\n", path);
 
     if (_this->gl_data->gl_active) {
-        SDL_SetError("OpenGL context already created");
-        return -1;
+        return SDL_SetError("OpenGL context already created");
     }
 
 
@@ -243,8 +241,7 @@ DirectFB_GL_MakeCurrent(_THIS, SDL_Window * window, SDL_GLContext context)
 int
 DirectFB_GL_SetSwapInterval(_THIS, int interval)
 {
-    SDL_Unsupported();
-    return -1;
+    return SDL_Unsupported();
 }
 
 int

src/video/directfb/SDL_DirectFB_render.c

@@ -657,8 +657,7 @@ DirectFB_SetTexturePalette(SDL_Renderer * renderer,
                          palette->SetEntries(data->palette, entries, ncolors, firstcolor));
         return 0;
     } else {
-        SDL_SetError("YUV textures don't have a palette");
-        return -1;
+        return SDL_SetError("YUV textures don't have a palette");
     }
   error:
     return -1;
@@ -688,8 +687,7 @@ DirectFB_GetTexturePalette(SDL_Renderer * renderer,
         }
         return 0;
     } else {
-        SDL_SetError("YUV textures don't have a palette");
-        return -1;
+        return SDL_SetError("YUV textures don't have a palette");
     }
   error:
     return -1;
@@ -718,9 +716,8 @@ DirectFB_SetTextureBlendMode(SDL_Renderer * renderer, SDL_Texture * texture)
     case SDL_BLENDMODE_MOD:
         return 0;
     default:
-        SDL_Unsupported();
         texture->blendMode = SDL_BLENDMODE_NONE;
-        return -1;
+        return SDL_Unsupported();
     }
 }
 
@@ -735,9 +732,8 @@ DirectFB_SetDrawBlendMode(SDL_Renderer * renderer)
     case SDL_BLENDMODE_MOD:
         return 0;
     default:
-        SDL_Unsupported();
         renderer->blendMode = SDL_BLENDMODE_NONE;
-        return -1;
+        return SDL_Unsupported();
     }
 }
 
@@ -762,10 +758,9 @@ DirectFB_SetTextureScaleMode(SDL_Renderer * renderer, SDL_Texture * texture)
             DSRO_SMOOTH_UPSCALE | DSRO_SMOOTH_DOWNSCALE | DSRO_ANTIALIAS;
         break;
     default:
-        SDL_Unsupported();
         data->render_options = DSRO_NONE;
         texture->scaleMode = SDL_SCALEMODE_NONE;
-        return -1;
+        return SDL_Unsupported();
     }
 #endif
     return 0;

src/video/directfb/SDL_DirectFB_window.c

@@ -176,8 +176,7 @@ DirectFB_CreateWindow(_THIS, SDL_Window * window)
 int
 DirectFB_CreateWindowFrom(_THIS, SDL_Window * window, const void *data)
 {
-    SDL_Unsupported();
-    return -1;
+    return SDL_Unsupported();
 }
 
 void
@@ -188,8 +187,9 @@ DirectFB_SetWindowTitle(_THIS, SDL_Window * window)
     if (windata->is_managed) {
         windata->wm_needs_redraw = 1;
         DirectFB_WM_RedrawLayout(_this, window);
-    } else
+    } else {
         SDL_Unsupported();
+    }
 }
 
 void