app: avoid reading uninitialized memory

gimp_rgb_to_hsl and hsl_to_rgb reads the a member, so set it before
calling them. Add gimp_hsl_set_alpha() for this purpose.

Found by coverity

app/operations/gimpcolorizeconfig.c

@@ -88,8 +88,8 @@ gimp_colorize_config_class_init (GimpColorizeConfigClass *klass)
                                    -1.0, 1.0, 0.0, 0);
 
   gimp_hsl_set (&hsl, 0.5, 0.5, 0.5);
+  gimp_hsl_set_alpha (&hsl, 1.0);
   gimp_hsl_to_rgb (&hsl, &rgb);
-  gimp_rgb_set_alpha (&rgb, 1.0);
 
   g_object_class_install_property (object_class, PROP_COLOR,
                                    gimp_param_spec_rgb ("color",
@@ -135,8 +135,8 @@ gimp_colorize_config_get_property (GObject    *object,
                       self->hue,
                       self->saturation,
                       (self->lightness + 1.0) / 2.0);
+        gimp_hsl_set_alpha (&hsl, 1.0);
         gimp_hsl_to_rgb (&hsl, &rgb);
-        gimp_rgb_set_alpha (&rgb, 1.0);
         gimp_value_set_rgb (value, &rgb);
       }
       break;

app/operations/gimpoperationcolorize.c

@@ -98,6 +98,7 @@ gimp_operation_colorize_process (GeglOperation       *operation,
 
   hsl.h = config->hue;
   hsl.s = config->saturation;
+  hsl.a = src[ALPHA];
 
   while (samples--)
     {
@@ -129,7 +130,7 @@ gimp_operation_colorize_process (GeglOperation       *operation,
       dest[RED]   = rgb.r; /* * lum; */
       dest[GREEN] = rgb.g; /* * lum; */
       dest[BLUE]  = rgb.b; /* * lum */;
-      dest[ALPHA] = src[ALPHA];
+      dest[ALPHA] = rgb.a;
 
       src  += 4;
       dest += 4;

app/operations/gimpoperationhuesaturation.c

@@ -162,6 +162,7 @@ gimp_operation_hue_saturation_process (GeglOperation       *operation,
       rgb.r = src[RED];
       rgb.g = src[GREEN];
       rgb.b = src[BLUE];
+      rgb.a = src[ALPHA];
 
       gimp_rgb_to_hsl (&rgb, &hsl);
 
@@ -253,7 +254,7 @@ gimp_operation_hue_saturation_process (GeglOperation       *operation,
       dest[RED]   = rgb.r;
       dest[GREEN] = rgb.g;
       dest[BLUE]  = rgb.b;
-      dest[ALPHA] = src[ALPHA];
+      dest[ALPHA] = rgb.a;
 
       src  += 4;
       dest += 4;

libgimpcolor/gimphsl.c

@@ -75,3 +75,19 @@ gimp_hsl_set (GimpHSL *hsl,
   hsl->s = s;
   hsl->l = l;
 }
+
+/**
+ * gimp_hsl_set_alpha:
+ * @hsl:
+ * @a:
+ *
+ * Since: GIMP 2.10
+ **/
+void
+gimp_hsl_set_alpha (GimpHSL *hsl,
+                    gdouble a)
+{
+  g_return_if_fail (hsl != NULL);
+
+  hsl->a = a;
+}

libgimpcolor/gimphsl.h

@@ -40,6 +40,8 @@ void    gimp_hsl_set        (GimpHSL *hsl,
                              gdouble  h,
                              gdouble  s,
                              gdouble  l);
+void    gimp_hsl_set_alpha  (GimpHSL *hsl,
+                             gdouble  a);
 
 
 G_END_DECLS