Use CircuitBuildTimeout whenever circuit_build_times_disabled is true

Previously, we checked LearnCircuitBuildTimeout directly.

Fixes bug #20073 in commit 5b0b51ca3 on tor 0.2.4.12-alpha.

changes/feature17178

@@ -18,3 +18,6 @@
     - Prevent Tor2web clients running hidden services, these services are
       not anonymous due to the one-hop client paths.
       Fixes bug #19678. Patch by teor.
+  o Minor bug fixes (circuits):
+    - Use CircuitBuildTimeout whenever LearnCircuitBuildTimeout is disabled.
+      Fixes bug #19678 in commit 5b0b51ca3 in 0.2.4.12-alpha. Patch by teor.

src/or/circuitstats.c

@@ -489,7 +489,7 @@ circuit_build_times_get_initial_timeout(void)
    */
   if (!unit_tests && get_options()->CircuitBuildTimeout) {
     timeout = get_options()->CircuitBuildTimeout*1000;
-    if (get_options()->LearnCircuitBuildTimeout &&
+    if (!circuit_build_times_disabled() &&
         timeout < circuit_build_times_min_timeout()) {
       log_warn(LD_CIRC, "Config CircuitBuildTimeout too low. Setting to %ds",
                circuit_build_times_min_timeout()/1000);