fix(gnovm): don't assert to bodyStmt when creating stacktraces (#3836)

Stacktraces being generated when executing a known statement, like the
initialization of an if statement, will have the panicking statement at
the top of the Stmt stack, which may not be a bodyStmt. This PR fixes
the incorrect assertion.

gnovm/pkg/gnolang/machine.go

@@ -388,8 +388,9 @@ func (m *Machine) Stacktrace() (stacktrace Stacktrace) {
 	for i := len(m.Frames) - 1; i >= 0; i-- {
 		if m.Frames[i].IsCall() {
 			stm := m.Stmts[nextStmtIndex]
-			bs := stm.(*bodyStmt)
-			stm = bs.Body[bs.NextBodyIndex-1]
+			if bs, ok := stm.(*bodyStmt); ok {
+				stm = bs.Body[bs.NextBodyIndex-1]
+			}
 			calls = append(calls, StacktraceCall{
 				Stmt:  stm,
 				Frame: m.Frames[i],

gnovm/tests/files/recover20.gno

@@ -0,0 +1,16 @@
+package main
+
+func main() {
+	var p *int
+	if i := *p; i == 0 {
+		println("hey")
+	}
+}
+
+// Error:
+// nil pointer dereference
+
+// Stacktrace:
+// panic: nil pointer dereference
+// main<VPBlock(1,0)>()
+//     main/files/recover20.gno:5