dthelp: Further coverity fixes

cde/programs/dthelp/parser/pass1/helptag/custom.c

@@ -210,7 +210,11 @@ SEARCH *searchp;
 char *mb_entcontent;
 
 mb_entcontent = MakeMByteString(entcontent);
-if (!*mb_entcontent) return NULL; /* null file name, don't open a directory */
+if (!*mb_entcontent)  /* null file name, don't open a directory */
+    {
+    m_free(mb_entcontent, "multi-byte string");
+    return NULL;
+    }
 
 open = fopen(mb_entcontent, "r");
 if (open)
@@ -301,7 +305,9 @@ void m_signmsg(p)
     if (q = strstr(p, VERSION)) {
       pCopy = strdup(p);
       q = strstr(pCopy, VERSION);
-      *q = M_EOS;
+      if(q) {
+        *q = M_EOS;
+      }
       m_errline(pCopy);
       free(pCopy);
       return;

cde/programs/dthelp/parser/pass1/helptag/help.if

@@ -870,9 +870,10 @@ static char ident6[]="@(#) (c) Copyright 1993, 1994 Unix System Labs, Inc., a su
     {
     char *mb_content, snb_id[32];
     char buffer[BIGBUF];
-    static M_WCHAR empty = M_EOS;
+    static M_WCHAR empty[1];
+    empty[0] = M_EOS;
 
-    if (!f_content) f_content = ∅
+    if (!f_content) f_content = empty;
 
     mb_content = MakeMByteString(f_content);
     sprintf(snb_id, "%s%d", sdlReservedName, NextId());

cde/programs/dthelp/parser/pass1/helptag/xref.c

@@ -153,6 +153,9 @@ FILE *tex;
 
 strcpy(helpext, ".xrh");
 tex = fopen(helpbase, "w");
+if (! tex) {
+	return;
+}
 fprintf(tex, "\\gobble\001%s\002%%\n", m_signon);
 fputs("% Generated Cross-Reference Macros (for a particular document)\n", tex);
 if (! xtree.data) {

cde/programs/dthelp/parser/pass1/util/malloc.c

@@ -93,7 +93,6 @@ void m_free(block, msg)
 #if defined(MSDOS)
     if (m_heapchk) m_heapdump() ;
 #endif
-    free(block) ;
     if (m_malftrace) {
 #if defined(hpux) || defined(_AIX) || defined(sun) || defined(USL) || defined(__uxp__)
       snprintf(buffer, 32, "%5x:%5x",
@@ -107,6 +106,7 @@ void m_free(block, msg)
       m_trace(msg) ;
       m_trace("\n") ;
       }      
+    free(block) ;
 #if defined(MSDOS)
     if (m_heapchk) m_heapdump() ;
 #endif