curl: Invalid write (or double free) triggers curl command line tool crash

Summary: Whilst fuzzing libcurl built from git commit a158a09, a crash triggered by an invalid write (or maybe a double/invalid free) was found. Steps To Reproduce: Run: echo "LVQvCnVyIDA=" | base64 -d > test0000 ./curl --verbose -q -K test0000 file:///dev/null Stack: valgrind -q src/curl --verbose -q -K ~/curl/tmp/out/crashes/test0001 file:///dev/null ==12371== Invalid free() / delete / delete[] / realloc() ==12371== at 0x48369AB: free (vg_replace_malloc.c:530) ==12371== by 0x128C84: add_file_name_to_url (in /root/curl-no-asan/src/curl) ==12371== by 0x1259EF: create_transfer (in /root/curl-no-asan/src/curl) ==12371== by 0x1285DC: operate (in /root/curl-no-asan/src/curl) ==12371== by 0x119828: main (in /root/curl-no-asan/src/curl) ==12371== Address 0x192f1a is in a r-- mapped file /root/curl-no-asan/src/curl segment ==12371== * Trying 0.0.0.0:80... % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0* connect to 0.0.0.0 port 80 failed: Connection refused * Failed to connect to 0 port 80: Connection refused 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0 * Closing connection 0 curl: (7) Failed to connect to 0 port 80: Connection refused * Closing connection 1 If we switch over to ASAN with AFL's libdislocator.so loaded: ```...