[Router] Fixed the Bug Causing Tons of Nightly Test Failures

The bug was introduced by me in commit 2966d66; I merged two adjacent
if-bodies with conditions that appeared the same, but were in fact not.

A simplified example is:
`if (A == 0) { ... A might be modified ... } if (A == 0) { return ; }`

Merging the if-bodies would be problematic if A is modified in the first
if-body and is no longer 0.

This mistake caused tons of nightly test failures, as mentioned in the
comments in PR#2720. So glad that the nightly tests CAUGHT this bug,
which was not detected by the VTR strong regression tests.

Author: ueqri

vpr/src/route/connection_router.cpp

@@ -159,7 +159,9 @@ std::tuple<bool, bool, RTExploredNode> ConnectionRouter<Heap>::timing_driven_rou
                                                                          sink_node,
                                                                          cost_params,
                                                                          net_bounding_box);
+    }
 
+    if (std::isinf(rr_node_route_inf_[sink_node].path_cost)) {
         VTR_LOG("%s\n", describe_unrouteable_connection(source_node, sink_node, is_flat_).c_str());
 
         heap_.empty_heap();