harden access to OUString[0]

Change-Id: Ibc2997f9974b8f6d561db0632642060ab95b80f0

vcl/source/window/builder.cxx

@@ -2807,7 +2807,7 @@ void VclBuilder::applyPackingProperty(Window *pCurrent,
 
             if (sKey == "expand")
             {
-                bool bTrue = (sValue[0] == 't' || sValue[0] == 'T' || sValue[0] == '1');
+                bool bTrue = (!sValue.isEmpty() && (sValue[0] == 't' || sValue[0] == 'T' || sValue[0] == '1'));
                 if (pToolBoxParent)
                     pToolBoxParent->SetItemExpand(m_pParserState->m_nLastToolbarId, bTrue);
                 else
@@ -2820,12 +2820,12 @@ void VclBuilder::applyPackingProperty(Window *pCurrent,
 
             if (sKey == "fill")
             {
-                bool bTrue = (sValue[0] == 't' || sValue[0] == 'T' || sValue[0] == '1');
+                bool bTrue = (!sValue.isEmpty() && (sValue[0] == 't' || sValue[0] == 'T' || sValue[0] == '1'));
                 pCurrent->set_fill(bTrue);
             }
             else if (sKey == "pack-type")
             {
-                VclPackType ePackType = (sValue[0] == 'e' || sValue[0] == 'E') ? VCL_PACK_END : VCL_PACK_START;
+                VclPackType ePackType = (!sValue.isEmpty() && (sValue[0] == 'e' || sValue[0] == 'E')) ? VCL_PACK_END : VCL_PACK_START;
                 pCurrent->set_pack_type(ePackType);
             }
             else if (sKey == "left-attach")

vcl/source/window/layout.cxx

@@ -1231,7 +1231,7 @@ void VclGrid::setAllocation(const Size& rAllocation)
 
 bool toBool(const OString &rValue)
 {
-    return (rValue[0] == 't' || rValue[0] == 'T' || rValue[0] == '1');
+    return (!rValue.isEmpty() && (rValue[0] == 't' || rValue[0] == 'T' || rValue[0] == '1'));
 }
 
 bool VclGrid::set_property(const OString &rKey, const OString &rValue)