dbStatic: Allow empty DB & DBD files

They used to cause a Syntax error with a bad context string.

documentation/RELEASE_NOTES.html

@@ -13,6 +13,13 @@
 
 <!-- Insert new items immediately below here ... -->
 
+<h4>Allow empty database files</h4>
+
+<p>The IOC used to report an error if dbLoadRecords or dbLoadDatabase was asked
+to load an empty file or one containing just whitespace and/or comments. Such
+files are now permitted, simplifying the task of automated database generation
+programs which might discover they have nothing to output.</p>
+
 <h4>High-Resolution Time Provider on MacOS</h4>
 
 <p>MacOS does not provide the clock_gettime() API with CLOCK_REALTIME that other

src/dbStatic/dbYacc.y

@@ -31,7 +31,13 @@ static int yyAbort = 0;
 
 %%
 
-database:	database database_item | database_item;
+database:	/* empty */
+	|	database_item_list
+	;
+
+database_item_list:	database_item_list database_item
+	|	database_item
+	;
 
 database_item:	include
 	|	path