Remove unnecessary null pointer checks

[elfring]

An extra null pointer check is not needed in functions like the following.

• prepare_specified_palette
• sixel_dither_destroy
• sixel_image_destroy

Would you like to add the following semantic patch approach to a test directory?

@Remove_unnecessary_pointer_checks1@
expression x;
@@
-if (\(x != 0 \| x != NULL\))
    free(x);

@Remove_unnecessary_pointer_checks2@
expression x;
@@
-if (\(x != 0 \| x != NULL\)) {
    free(x);
    x = \(0 \| NULL\);
-}

@Remove_unnecessary_pointer_checks3@
expression a, b;
@@
-if (\(a != 0 \| a != NULL\) && \(b != 0 \| b != NULL\))
+if (a)
    free(b);

@Remove_unnecessary_pointer_checks4@
expression a, b;
@@
-if (\(a != 0 \| a != NULL\) && \(b != 0 \| b != NULL\)) {
+if (a) {
    free(b);
    b = \(0 \| NULL\);
 }

How do you think about to apply a corresponding update suggestion which will eventually be generated by the software "Coccinelle"?

[saitoha]

@elfring Fixed. Would this be OK?

[elfring]

Thanks for your small source code improvement.

How do you think about to extend this software update with another clean-up? Would you like to add input parameter validation for functions like "sixel_…_destroy" and "sixel_…_unref" so that corresponding pointer checks can also be deleted directly before their calls?

[saitoha]

@elfring Thanks! I added that things. https://github.com/saitoha/libsixel/compare/fix-issue-6

[saitoha]

fixed.