fix: add missing include for stdlib.h

[maxice8]

fixes compilation on Alpine Linux x86/armhf/armv7

error: implicit declaration of function 'malloc' -Werror=implicit-function-declaration 83 | fade->original_buffer = malloc(size); | ^~[ ../fade.c:83:26: error: incompatible implicit declaration of built-in function 'malloc' -Werror ../fade.c:8:1: note: include '' or provide a declaration of 'malloc' 7 | #include +++ | #include 8 |

[mortie]

Thanks!