truename: fix array overrun [fixes #212]

src[-2] was peeking into a random memory location.
It seems entire truename() is written by some morons... :(
Its completely unreadable and full of bugs.

kernel/newstuff.c

@@ -186,7 +186,10 @@ long DosMkTmp(char FAR * pathname, UWORD attr)
 
 */
 
-#define PATH_ERROR goto errRet
+#define PATH_ERROR() \
+      fstrchr(src, '/') == 0 && fstrchr(src, '\\') == 0 \
+        ? DE_FILENOTFND \
+        : DE_PATHNOTFND
 #define PATHLEN 128
 
 
@@ -244,7 +247,7 @@ STATIC const char _DirChars[] = "\"[]:|<>+=;,";
 
 #define addChar(c) \
 { \
-  if (p >= dest + REMOTE_PATH_MAX) PATH_ERROR; /* path too long */	\
+  if (p >= dest + REMOTE_PATH_MAX) return PATH_ERROR(); /* path too long */	\
   *p++ = c; \
 }
 
@@ -479,14 +482,18 @@ COUNT truename(__XFAR(const char) src, char FAR *dest, COUNT mode)
 
     if(*src == '.')
     {
+      int dots = 1;
       /* special directory component */
       ++src;
       if (*src == '.') /* skip the second dot */
+      {
         ++src;
+        dots++;
+      }
       if (*src == '/' || *src == '\\' || *src == '\0')
       {
         --p; /* backup the backslash */
-        if (src[-2] == '.')
+        if (dots == 2)
         {
           /* ".." entry */
           /* remove last path component */
@@ -498,12 +505,9 @@ COUNT truename(__XFAR(const char) src, char FAR *dest, COUNT mode)
       }
 
       /* ill-formed .* or ..* entries => return error */
-    errRet:
       /* The error is either PATHNOTFND or FILENOTFND
          depending on if it is not the last component */
-      return fstrchr(src, '/') == 0 && fstrchr(src, '\\') == 0
-        ? DE_FILENOTFND
-        : DE_PATHNOTFND;
+      return PATH_ERROR();
     }
 
     /* normal component */
@@ -536,7 +540,7 @@ COUNT truename(__XFAR(const char) src, char FAR *dest, COUNT mode)
       if (c == '.')
       {
         if (state & PNE_DOT) /* multiple dots are ill-formed */
-          PATH_ERROR;
+          return PATH_ERROR();
         /* strip trailing dot */
         if (*src == '/' || *src == '\\' || *src == '\0')
           break;
@@ -548,7 +552,7 @@ COUNT truename(__XFAR(const char) src, char FAR *dest, COUNT mode)
         state |= PNE_WILDCARD;
       if (i) {	/* name length in limits */
         --i;
-        if (!DirChar(c)) PATH_ERROR;
+        if (!DirChar(c)) return PATH_ERROR();
         addChar(c);
       }
     }