plug-ins, operations: Fix warnings on Windows

This patch reduces three sets of warnings
when compiling on Windows:

* In gimp-layer-modes.c, we move the
g_return_val_if_reached () in
gimp_layer_mode_get_format () to the
default case in the last switch statement
to prevent a warning about an unhandled
switch case

* In spline.c, we initialize V[] to prevent
a warning about uninitialized values

* In flame.c, we unconditionally call
g_bytes_unref () to prevent a warning
about dangling pointers.

app/operations/layer-modes/gimp-layer-modes.c

@@ -1541,9 +1541,10 @@ gimp_layer_mode_get_format (GimpLayerMode           mode,
 
     case GIMP_LAYER_COLOR_SPACE_LAB:
       return babl_format_with_space ("CIE Lab alpha float", preferred_format);
-    }
 
-  g_return_val_if_reached (babl_format_with_space ("RGBA float", preferred_format));
+    default:
+      g_return_val_if_reached (babl_format_with_space ("RGBA float", preferred_format));
+    }
 }
 
 GimpLayerCompositeRegion

plug-ins/flame/flame.c

@@ -1034,13 +1034,10 @@ set_flame_preview (GimpProcedureConfig *proc_config)
     return;
 
   g_object_get (proc_config, "settings-data", &settings_bytes, NULL);
-  if (settings_bytes != NULL)
-    {
-      if (g_bytes_get_size (settings_bytes) == sizeof (FlameSettings))
-        config = *((FlameSettings *) g_bytes_get_data (settings_bytes, NULL));
-
-      g_bytes_unref (settings_bytes);
-    }
+  if (settings_bytes != NULL &&
+      g_bytes_get_size (settings_bytes) == sizeof (FlameSettings))
+    config = *((FlameSettings *) g_bytes_get_data (settings_bytes, NULL));
+  g_bytes_unref (settings_bytes);
 
   g_object_get (proc_config,
                 "x",                     &config.cp.center[0],

plug-ins/selection-to-path/spline.c

@@ -83,6 +83,9 @@ evaluate_spline (spline_type s, real t)
   real one_minus_t = 1.0 - t;
   polynomial_degree degree = SPLINE_DEGREE (s);
 
+  for (i = 0; i < 4; i++)
+    V[i] = new_spline ();
+
   for (i = 0; i <= degree; i++)
     V[0].v[i] = s.v[i];