delv isc_app_ctxsuspend ctx->running ASSERTION

[Steve Egbert]

>> Had an assertion error for `delv` utility in trying to perform suspend 
>> thread.
>>
>> Doesn't seem specific to any thing, argument-wise.
>>

This is weird.

`*ctx->running` is set to `true`.

It would have continued on normally to suspending the thread, if it 
weren't for that `REQUIRE(VALID_APPCTX(ctx));` logic.

Using:
* gcc 8.3.0
* ld (GNU Binutils 2.31.1)
* ISC library 1701
* ISCCFG library 1700
* ISCCC library 1700
* IRC library 1700


Full GNU gcc version output:
```console
# gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/8/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 8.3.0-6' 
--with-bugurl=file:///usr/share/doc/gcc-8/README.Bugs 
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ 
--prefix=/usr --with-gcc-major-version-only --program-suffix=-8 
--program-prefix=x86_64-linux-gnu- --enable-shared 
--enable-linker-build-id --libexecdir=/usr/lib 
--without-included-gettext --enable-threads=posix --libdir=/usr/lib 
--enable-nls --enable-bootstrap --enable-clocale=gnu 
--enable-libstdcxx-debug --enable-libstdcxx-time=yes 
--with-default-libstdcxx-abi=new --enable-gnu-unique-object 
--disable-vtable-verify --enable-libmpx --enable-plugin 
--enable-default-pie --with-system-zlib --with-target-system-zlib 
--enable-objc-gc=auto --enable-multiarch --disable-werror 
--with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 
--enable-multilib --with-tune=generic 
--enable-offload-targets=nvptx-none --without-cuda-driver 
--enable-checking=release --build=x86_64-linux-gnu 
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 8.3.0 (Debian 8.3.0-6)
```