lalr1.cc: check (and fix) %initial-action exception safety

* data/lalr1.cc: Check size > 1, rather than size != 1, when cleaning
the stack, as at the beginning, size is 0.
* tests/c++.at (Exception safety): Check exception safety in
%initial-action.

data/lalr1.cc

@@ -828,7 +828,7 @@ m4_ifdef([b4_lex_param], [, ]b4_lex_param))[;
     /* Do not reclaim the symbols of the rule which action triggered
        this YYABORT or YYACCEPT.  */
     yypop_ (yylen);
-    while (yystate_stack_.height () != 1)
+    while (1 < yystate_stack_.height ())
       {
         yydestruct_ ("Cleanup: popping",
                      yystos_[yystate_stack_[0]],
@@ -852,7 +852,7 @@ m4_ifdef([b4_lex_param], [, ]b4_lex_param))[;
                          &yylloc);
           }
 
-        while (yystate_stack_.height () != 1)
+        while (1 < yystate_stack_.height ())
           {
             yydestruct_ ("Cleanup: popping",
                          yystos_[yystate_stack_[0]],

tests/c++.at

@@ -226,6 +226,7 @@ AT_DATA_GRAMMAR([[input.yy]],
 %code
 {
   #include <cassert>
+  #include <cstring> // strchr
   #include <stdexcept>
   int yylex (yy::parser::semantic_type *);
   size_t Object::counter = 0;
@@ -237,6 +238,12 @@ AT_DATA_GRAMMAR([[input.yy]],
   Object* obj;
 }
 
+%initial-action
+{
+  if (strchr (input, 'i'))
+    throw std::runtime_error ("initial-action");
+}
+
 %destructor { delete $$; } <obj>;
 %printer { yyo << "counter == " << $$->counter; } <obj>;
 
@@ -260,7 +267,7 @@ item:
 | 's'
   {
     std::swap ($$, $1);
-    throw std::runtime_error ("invalid expression");
+    throw std::runtime_error ("reduction");
   }
 
 %%
@@ -268,11 +275,14 @@ item:
 int
 yylex (yy::parser::semantic_type *lvalp)
 {
-  // 'l': lexical exception, 's': syntactic exception.
+  // 'a': no error.
+  // 'i': initial action throws.
+  // 'l': yylex throws.
+  // 's': reduction throws.
   switch (int res = *input++)
   {
     case 'l':
-      throw std::runtime_error ("invalid character");
+      throw std::runtime_error ("yylex");
     default:
       lvalp->obj = new Object;
       // Fall through.
@@ -312,11 +322,15 @@ AT_BISON_CHECK([[-o input.cc input.yy]])
 AT_COMPILE_CXX([[input]])
 
 AT_PARSER_CHECK([[./input aaaas]], [[2]], [[]],
-[[exception caught: invalid expression
+[[exception caught: reduction
 ]])
 
 AT_PARSER_CHECK([[./input aaaal]], [[2]], [[]],
-[[exception caught: invalid character
+[[exception caught: yylex
+]])
+
+AT_PARSER_CHECK([[./input i]], [[2]], [[]],
+[[exception caught: initial-action
 ]])
 
 AT_BISON_OPTION_POPDEFS