Asserting rtl::O[U]StringBuffer::operator [] preconditions

...and fixing two call-sites.

Change-Id: I8ed8cb189bd5034130b49b2f57156568e6b24716

sal/inc/rtl/strbuf.hxx

@@ -417,7 +417,11 @@ public:
 
       @since LibreOffice 3.5
     */
-    sal_Char & operator [](sal_Int32 index) { return pData->buffer[index]; }
+    sal_Char & operator [](sal_Int32 index)
+    {
+        assert(index >= 0 && index < pData->length);
+        return pData->buffer[index];
+    }
 
     /**
         Return a OString instance reflecting the current content

sal/inc/rtl/ustrbuf.hxx

@@ -409,7 +409,11 @@ public:
 
       @since LibreOffice 3.5
     */
-    sal_Unicode & operator [](sal_Int32 index) { return pData->buffer[index]; }
+    sal_Unicode & operator [](sal_Int32 index)
+    {
+        assert(index >= 0 && index < pData->length);
+        return pData->buffer[index];
+    }
 
     /**
         Return a OUString instance reflecting the current content

svl/source/numbers/zformat.cxx

@@ -1522,7 +1522,9 @@ short SvNumberformat::ImpNextSymbol(OUStringBuffer& rString,
                 OUString aUpperDBNum( rChrCls().uppercase( rString.toString(), nPos-1, aDBNum.getLength() ) );
                 sal_Unicode cUpper = aUpperNatNum[0];
                 sal_Int32 nNatNumNum = rString.toString().copy( nPos - 1 + aNatNum.getLength() ).toInt32();
-                sal_Unicode cDBNum = rString[ nPos - 1 + aDBNum.getLength()];
+                sal_Unicode cDBNum =
+                    nPos - 1 + aDBNum.getLength() < rString.getLength()
+                    ? rString[nPos - 1 + aDBNum.getLength()] : 0;
                 if ( aUpperNatNum == aNatNum && 0 <= nNatNumNum && nNatNumNum <= 19 )
                 {
                     sBuffSymbol.stripStart((sal_Unicode)'[');

vcl/source/control/field2.cxx

@@ -2265,7 +2265,7 @@ static sal_Bool ImplTimeGetValue( const OUString& rStr, Time& rTime,
             return sal_False;
 
         nSepPos = aStr.indexOf( rLocaleDataWrapper.getTimeSep() );
-        if ( aStr[0] == '-' )
+        if ( !aStr.isEmpty() && aStr[0] == '-' )
             bNegative = sal_True;
         if ( nSepPos >= 0 )
         {