Allow the user paperspecs file to be invalid

Assume the system file is valid. Some clients can crash in this case,
because they do not check the return value of paperinit().

lib/libpaper.c.in.in

@@ -164,10 +164,8 @@ const struct paper *papernext(const struct paper *paper)
 }
 
 /* Constructor. */
-static int readspecs(struct paper **papers_list, const char *specsfile, struct paper **last) {
-    paper_lineno = 0;
-    free(paper_specsfile);
-    paper_specsfile = strdup(specsfile);
+static int readspecs(struct paper **papers_list, const char *specsfile, struct paper **last, size_t *lineno) {
+    *lineno = 0;
     char *old_locale = setlocale(LC_ALL, NULL);
     if (old_locale != NULL)
         old_locale = strdup(old_locale);
@@ -178,7 +176,7 @@ static int readspecs(struct paper **papers_list, const char *specsfile, struct p
         struct paper *prev = *papers_list, *p;
         size_t n;
         char *l;
-        for (paper_lineno = 1, l = NULL; getline(&l, &n, ps) > 0; prev = p, paper_lineno++) {
+        for (*lineno = 1, l = NULL; getline(&l, &n, ps) > 0; prev = p, (*lineno)++) {
             char *saveptr;
             char *name = gettok(l, &saveptr);
             char *wstr = gettok(NULL, &saveptr), *hstr = gettok(NULL, &saveptr);
@@ -350,19 +348,18 @@ int paperinit(void)
         return PAPER_OK;
     initialized = true;
 
+    int ret = PAPER_OK;
+
     /* Read system paperspecs. */
     struct paper *system_papers = NULL;
     sysconfdir = alloc_relocate("@sysconfdir@");
     if (sysconfdir != NULL) {
         char *system_paperspecs = mfile_name_concat(sysconfdir, PAPERSPECS_FILENAME, NULL);
         if (system_paperspecs == NULL)
             return PAPER_NOMEM;
-        int ret = readspecs(&system_papers, system_paperspecs, NULL);
-        free(system_paperspecs);
-        if (ret != PAPER_OK) {
-            paperdone();
-            return ret;
-        }
+        ret = readspecs(&system_papers, system_paperspecs, NULL, &paper_lineno);
+        free(paper_specsfile);
+        paper_specsfile = system_paperspecs;
     }
 
     /* Set default paper to first system paper, if any. */
@@ -381,11 +378,15 @@ int paperinit(void)
     char *user_paperspecs = mfile_name_concat(xdg_config_home, PAPERSPECS_FILENAME, NULL);
     struct paper *last_paper = NULL;
     if (user_paperspecs != NULL) {
-        int ret = readspecs(&papers, user_paperspecs, &last_paper);
-        free(user_paperspecs);
-        if (ret != PAPER_OK) {
-            paperdone();
-            return ret;
+        size_t user_lineno;
+        int user_ret = readspecs(&papers, user_paperspecs, &last_paper, &user_lineno);
+        if (ret == PAPER_OK) {
+            ret = user_ret;
+            free(user_paperspecs);
+        } else if (paper_lineno == 0) {
+            free(paper_specsfile);
+            paper_specsfile = user_paperspecs;
+            paper_lineno = user_lineno;
         }
     }
 
@@ -395,13 +396,16 @@ int paperinit(void)
             default_paper = papers;
 
         /* Concatenate system papers to user papers. */
-        last_paper->next = system_papers;
+        if (last_paper != NULL)
+            last_paper->next = system_papers;
+        else
+            last_paper = system_papers;
     }
 
     if (papers == NULL) /* System papers are all we have. */
         papers = system_papers;
 
-    return PAPER_OK;
+    return ret;
 }
 
 /* Shut down the library. */