ColorPalette: Fix Dispose function

* Set freed pointer to NULL in dispose function because dispose cna be run multiple times. This fixes the case of freeing an already freed pointer.

doxygen/compilation.dox

@@ -30,7 +30,7 @@ Development is done with the following library versions:
 
 | Cairographics | GLib2      | GTK3      |
 | ------------- | ---------- | --------- |
-| 1.17.3        | 2.60.6-1   | 3.24.10-1 |
+| 1.17.2        | 2.64.2     | 3.24.18   |
 
 @section comp-instr Compilation Instructions
 @subsection linux-build General Linux Build Instruction
@@ -59,7 +59,7 @@ The subfolder 'AUR' contains a PKGBUILD file to build an Archlinux/Pacman packag
 
 @subsection comp-warnings Compiler Warnings
 
-The compiler will throw the following warnings. Compiled with GCC 8.2.1.
+The compiler will throw the following warnings. Compiled with GCC 9.3.0.
 
 | Warning | Assessment |
 | ------- | ---------- |

geometric/vector-operations.c

@@ -65,7 +65,7 @@ void vector_2d_rotate(struct vector_2d *vec, double angle)
 	sin_val = sin(angle);
 	cos_val = cos(angle);
 
-	vector_2d_copy(&temp, vec);
+	(void)vector_2d_copy(&temp, vec);
 
 	/* Apply rotation matrix */
 	vec->x = (cos_val * temp.x) - (sin_val * temp.y);

layer/color-palette.c

@@ -238,6 +238,7 @@ static void color_palette_dispose(GObject *gobj)
 	if (palette->color_array) {
 		palette->color_array_length = 0;
 		free(palette->color_array);
+		palette->color_array = NULL;
 	}
 
 	/* Chain up to parent class */