Optimize and deduplicate code in ParamIterator()

Don't create and assign to d->m_prefix two QString objects if the paren
is not closed. m_prefix is used only in ParamIterator::prefix(), which
in turn is not used by ParamIterator itself, so the code reordering does
not change behavior.

kdevplatform/language/duchain/stringhelpers.cpp

@@ -335,19 +335,16 @@ ParamIterator::ParamIterator(const QString& parens, const QString& source, int o
     } else {
         if (parenBegin != -1) {
             //We have a valid prefix before an opening-paren. Take the prefix, and start iterating parameters.
-            d->m_prefix = d->m_source.mid(offset, parenBegin - offset);
             d->m_cur = parenBegin + 1;
             d->m_curEnd = d->next();
-            if (d->m_curEnd == d->m_source.length()) {
-                //The paren was not closed. It might be an identifier like "operator<", so count everything as prefix.
-                d->m_prefix = d->m_source.mid(offset);
-                d->m_curEnd = d->m_end = d->m_cur = d->m_source.length();
-            }
-        } else {
-            //We have neither found an ending-character, nor an opening-paren, so take the whole input and end
-            d->m_prefix = d->m_source.mid(offset);
-            d->m_curEnd = d->m_end = d->m_cur = d->m_source.length();
-        }
+            if (d->m_curEnd != d->m_source.length()) {
+                d->m_prefix = d->m_source.mid(offset, parenBegin - offset);
+                return;
+            } // else: the paren was not closed. It might be an identifier like "operator<", so count everything as prefix.
+        } // else: we have neither found an ending-character, nor an opening-paren, so take the whole input and end.
+
+        d->m_prefix = d->m_source.mid(offset);
+        d->m_curEnd = d->m_end = d->m_cur = d->m_source.length();
     }
 }