lex.c: restore lexd.nested_tilde flag & handling (re: c40851a)

Removing that flag was a mistake, because it serves another
purpose: if it is set, the 'continue' on line 700 is executed,
avoiding the 'goto epat' online 704 or the state table change to
ST_NORM on line 706 when we're within ~(...) within ${...}.

Author: McDutchie

src/cmd/ksh93/include/shlex.h

@@ -50,6 +50,7 @@ struct _shlex_pvt_lexdata_
 	char		dolparen_arithexp;	/* set while comsub() is lexing an arithmetic expansion */
 	char		nest;
 	char		docword;
+	char		nested_tilde;
 	char 		*docend;
 	char		inlexskip;	/* set when sh_lex() is called from sh_lexskip() */
 	char		warn;

src/cmd/ksh93/include/version.h

@@ -18,7 +18,7 @@
 #include <ast_release.h>
 #include "git.h"
 
-#define SH_RELEASE_DATE	"2025-06-08"	/* must be in this format for $((.sh.version)) */
+#define SH_RELEASE_DATE	"2025-06-09"	/* must be in this format for $((.sh.version)) */
 /*
  * This comment keeps SH_RELEASE_DATE a few lines away from SH_RELEASE_SVER to avoid
  * merge conflicts when cherry-picking dev branch commits onto a release branch.

src/cmd/ksh93/sh/lex.c

@@ -660,7 +660,10 @@ int sh_lex(Lex_t* lp)
 				if(c=='~' && mode==ST_NESTED)
 				{
 					if(endchar(lp)==RBRACE)
+					{
+						lp->lexd.nested_tilde++;
 						goto tilde;
+					}
 					continue;
 				}
 				/* FALLTHROUGH */
@@ -683,9 +686,19 @@ int sh_lex(Lex_t* lp)
 				n = fcgetc();
 				if(n>0)
 				{
-					if(c=='~' && n==LPAREN && lp->lex.incase)
-						lp->lex.incase = TEST_RE;
+					if(c=='~' && n==LPAREN)
+					{
+						if(lp->lexd.nested_tilde)
+							lp->lexd.nested_tilde++;
+						else if(lp->lex.incase)
+							lp->lex.incase = TEST_RE;
+					}
 					fcseek(-LEN);
+					if(lp->lexd.nested_tilde)
+					{
+						lp->lexd.nested_tilde--;
+						continue;
+					}
 				}
 				if(n==LPAREN)
 					goto epat;
@@ -1063,6 +1076,8 @@ int sh_lex(Lex_t* lp)
 						fcseek(-LEN);
 					n = RPAREN;
 				}
+				if(c==RBRACE)
+					lp->lexd.nested_tilde = 0;
 				if(c==';' && n!=';')
 					continue;
 				if(mode==ST_QNEST)