Error if 'yahooj' symbol has no data

The while() loop never terminates if there is no table matching the
xpath used to create 'rows'. Break if there is less than one row, and
then throw an error.

Fixes #63.

R/getSymbols.R

@@ -499,13 +499,17 @@ function(Symbols,env,return.class='xts',index.class="Date",
 
                 fdoc <- XML::htmlParse(tmp)
                 rows <- XML::xpathApply(fdoc, "//table[@class='boardFin yjSt marB6']//tr")
-                if (length(rows) == 1) break
+                if (length(rows) <= 1) break
 
                 totalrows <- c(totalrows, rows)
                 page <- page + 1
             }
             if(verbose) cat("done.\n")
 
+            if (is.null(rows)) {
+              stop("No historical data for ", dQuote(Symbols[[i]]), ".")
+            }
+
             # Available columns
             cols <- c('Open','High','Low','Close','Volume','Adjusted')