FIR CFG: correct edge label from a node that returns Nothing

If it's not within a try/catch/finally, that should be an uncaught
exception path.

^KT-45327 Fixed

compiler/fir/analysis-tests/testData/resolve/cfg/jumps.dot

@@ -72,7 +72,7 @@ digraph jumps_kt {
     15 -> {16};
     16 -> {17};
     17 -> {18};
-    18 -> {29};
+    18 -> {29}    [label=onUncaughtException];
     18 -> {19} [style=dotted];
     19 -> {20} [style=dotted];
     20 -> {21} [style=dotted];