Invalid id possible with tooltips

In case a filename starts with a number the `id` also starts with a number and this is not allowed in XHTML and results in the message:
`Syntax of value for attribute id of div is not valid`
on other places it has been solved by placing an `a` as first character, this is done here as well but also needs to be don in the transformation from reference to tooltip id (htmlgen.cpp)

1 files changed, 1 insertions, 0 deletions

diff --git a/src/tooltip.cpp b/src/tooltip.cpp
index 3b128a9..91da583 100644
--- a/src/tooltip.cpp
+++ b/src/tooltip.cpp
@@ -84,6 +84,7 @@ void TooltipManager::addTooltip(Definition *d)
   {
     id+="_"+anc;
   }
+  id = "a" + id;
   if (p->tooltipInfo.find(id)==0)
   {
     p->tooltipInfo.insert(id,d);