Created attachment 3774 [details]
poc

## IMG_LoadPCX_RW@IMG_pcx.c:178-24___SEGV_UNKNOW

### description

    An issue was discovered in libsdl2 2.0.9 with SDL2_image-2.0.4 , There is a null-pointer-dereference in function IMG_LoadPCX_RW at IMG_pcx.c:178-24

### commandline

    loadtif  @@ 

### source

```c
 174                         }
 175                     } else
 176                         count = 1;
 177                 }
> 178                 dst[i] = ch;
 179                 count--;
 180             }
 181         }
 182 
 183         if(src_bits <= 4) {

// loadtif.c
// #include <stdio.h>
// #include <SDL.h>
// #include <SDL_image.h>
//
// int main(int argc, char * argv[]){
//         IMG_Init(IMG_INIT_TIF);//IMG_INIT_JPG);IMG_INIT_PNG
//         while(__AFL_LOOP(1000)){
//               SDL_Surface * image = IMG_Load(argv[1]);
//               if (image){
//                 SDL_FreeSurface(image);
//               }
//         }
//         IMG_Quit();
// }
```

### bug report

```txt
ASAN:DEADLYSIGNAL
=================================================================
==13991==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x7fd7bb11fabf bp 0x7ffe60cd2650 sp 0x7ffe60cd23e0 T0)
    #0 0x7fd7bb11fabe in IMG_LoadPCX_RW /src/SDL2_image-2.0.4/IMG_pcx.c:178:24
    #1 0x7fd7bb10e9bd in IMG_LoadTyped_RW /src/SDL2_image-2.0.4/IMG.c:195:17
    #2 0x7fd7bb10df41 in IMG_Load /src/SDL2_image-2.0.4/IMG.c:136:12
    #3 0x4ea0f0 in main /src/loadtif.c:8:37
    #4 0x7fd7b9c1482f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)
    #5 0x4189e8 in _start (/src/aflbuild/installed/bin/loadtif+0x4189e8)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV /src/SDL2_image-2.0.4/IMG_pcx.c:178:24 in IMG_LoadPCX_RW
==13991==ABORTING

```

### others

    from fuzz project pwd-libsdl2-loadtif-00
    crash name pwd-libsdl2-loadtif-00-00000004-20190419.tif
    Auto-generated by pyspider at 2019-04-19 00:07:04