Use the last value for all unspecified pages per row

This change ensures that configs with "first-page-column=2" before 0.3.4 will
upgrade more sanely.
Signed-off-by: Sebastian Ramacher <sebastian+dev@ramacher.at>

doc/man/zathurarc.5.rst

@@ -739,8 +739,11 @@ first-page-column
 ^^^^^^^^^^^^^^^^^
 Defines the column in which the first page will be displayed.
 This setting is stored separately for every value of pages-per-row according to
-the following pattern <1 page per row>:[<2 pages per row>[: ...]]. Per default,
-the first column is set to 2 for double-page layout.
+the following pattern <1 page per row>:[<2 pages per row>[: ...]]. The last
+value in the list will be used for all other number of pages per row if not set
+explicitely.
+
+Per default, the first column is set to 2 for double-page layout.
 
 * Value type: String
 * Default value: 1:2

zathura/utils.c

@@ -269,6 +269,8 @@ find_first_page_column(const char* first_page_column_list,
   unsigned int index = pages_per_row - 1;
   if (index < settings_size && *settings[index] != '\0') {
     first_page_column = atoi(settings[index]);
+  } else if (*settings[settings_size - 1] != '\0') {
+    first_page_column = atoi(settings[settings_size - 1]);
   }
 
   /* free buffers */