Fixed segfault on spacey input.

src/ast.c

@@ -88,7 +88,10 @@ void ast_destroy_psv(AST* ast) {
     free(ast);
 }
 
-void ast_print(AST* ast) { ast_print_i(ast, 0); }
+void ast_print(AST* ast) {
+    if (!ast) return;
+    ast_print_i(ast, 0);
+}
 
 void ast_print_i(AST* ast, int i) {
     INDENT_BEGIN(i);

src/exec.c

@@ -13,6 +13,8 @@
 AST* exec_start(AST* ast) {
     log_dbg("Started execution.");
 
+    if (!ast) return ast;
+
     Scope* global = scope_init(NULL);
     global->uses = 1;