logic analyzer: fix annotation empty string causing infinite loop

- Handle the edge case where an empty string passed to the shortenAnnotationText
function causes an infinite loop.
This fix ensures that the function returns the extension ("...") when the
text is empty or the maxWidth is too small to fit the extension.

Signed-off-by: Adrian Stanea <[email protected]>

plugins/m2k/m2k-gui/sigrok-gui/src/annotationcurve.cpp

@@ -672,16 +672,27 @@ uint64_t AnnotationCurve::getMaxAnnotationCount(int index)
 // shorten text to fit maxWidth pixels in width
 QString AnnotationCurve::shortenAnnotationText(const QString text, const double maxWidth, QPainter *painter) const
 {
-	const int padding = 12;
-	const QString extension = "...";
+	const int PADDING = 12;
+	const QString EXTENSION = "...";
 	int count = 0;
 
+	bool isWithinTextLength = true;
+	bool isWithinMaxWidth = true;
+
+	// Empty text or maxWidth is too small to even fit the extension
+	if(text.isEmpty() || maxWidth <= PADDING + painter->fontMetrics().horizontalAdvance(EXTENSION)) {
+		return EXTENSION;
+	}
+
 	// find maximum number of characters that fit
-	while(QSizeF(QwtText(text.left(count) + extension).textSize(painter->font())).width() <= maxWidth - padding) {
+	while(isWithinTextLength && isWithinMaxWidth) {
 		count++;
+		isWithinTextLength = count < text.length();
+		isWithinMaxWidth = QSizeF(QwtText(text.left(count) + EXTENSION).textSize(painter->font())).width() <=
+			maxWidth - PADDING;
 	}
 
-	return count ? text.left(count) + extension : "";
+	return isWithinTextLength ? text.left(count) + EXTENSION : "";
 }
 
 void AnnotationCurve::drawTwoSampleAnnotation(int row, const Annotation &ann, QPainter *painter,