trurl: use curl_free() on a pointer coming from curl_maprintf()

One instance of a pointer coming from curl_maprintf() was freed with a
normal free() which breaks and causes ASAN/valgrind to complain when
using a debug-enabled libcurl. Since the function could return a normal
heap-allocated pointer or a curl-allocated one, copy the string and
curl_free() the original.

Closes #393

Author: dfandrich

trurl.c

@@ -1381,6 +1381,7 @@ static struct string *memdupzero(char *source, size_t len, bool *modified)
       int rlen;
       int leftside;
       int rightside;
+      char *dupencode;
 
       /* decode both sides */
       leftside = (int)(sep - source);
@@ -1423,6 +1424,12 @@ static struct string *memdupzero(char *source, size_t len, bool *modified)
       encode = curl_maprintf("%s=%s", el ? el : "", er ? er : "");
       if(!encode)
         goto error;
+      /* pointers from curl_maprintf() must be curl_free()d so make a copy */
+      dupencode = strdup(encode);
+      curl_free(encode);
+      encode = dupencode;
+      if(!encode)
+        goto error;
     }
     olen = (int)strlen(encode);