FIR DFA: make continue jump to condition entry, not loop entry

It's also not a backwards jump in do-while, unless it's in the loop's
condition, which is a stupid "feature" IMO. As you can probably tell
from the comments added in this commit.

compiler/fir/analysis-tests/testData/resolve/smartcasts/boundSmartcasts/boundSmartcastsInBranches.dot

@@ -136,7 +136,7 @@ digraph boundSmartcastsInBranches_kt {
     36 -> {37};
     37 -> {38};
     38 -> {39} [style=dotted];
-    38 -> {17} [color=green style=dashed];
+    38 -> {18} [color=green style=dashed];
     39 -> {40} [style=dotted];
     40 -> {41} [style=dotted];
     41 -> {42} [style=dotted];