Debugger: Fix #11669.

SourceView:
- When calculating line widths for scrollbar calculation purposes, tabstop
  offsets weren't being correctly taken into account, which would result
  in lines being computed as shorter than they actually were. Depending
  on the content of the file, the horizontal scrollbar would consequently
  be configured improperly in some cases.

src/apps/debugger/user_interface/gui/team_window/SourceView.cpp

@@ -330,6 +330,8 @@ private:
 			};
 
 			float				_MaxLineWidth();
+	inline	float				_FormattedLineWidth(const char* line) const;
+
 			void				_DrawLineSyntaxSection(const char* line,
 									int32 length, int32& _column,
 									BPoint& _offset);
@@ -1523,16 +1525,30 @@ SourceView::TextView::_MaxLineWidth()
 
 	fMaxLineWidth = 0;
 	if (fSourceCode != NULL) {
-		for (int32 i = 0; const char* line = fSourceCode->LineAt(i); i++) {
-			fMaxLineWidth = std::max(fMaxLineWidth,
-				fFontInfo->font.StringWidth(line));
-		}
+		for (int32 i = 0; const char* line = fSourceCode->LineAt(i); i++)
+			fMaxLineWidth = std::max(fMaxLineWidth, _FormattedLineWidth(line));
 	}
 
 	return fMaxLineWidth;
 }
 
 
+float
+SourceView::TextView::_FormattedLineWidth(const char* line) const
+{
+	int32 column = 0;
+	int32 i = 0;
+	for (; line[i] != '\0'; i++) {
+		if (line[i] == '\t')
+			column = _NextTabStop(column);
+		else
+			++column;
+	}
+
+	return column * fCharacterWidth;
+}
+
+
 void
 SourceView::TextView::_DrawLineSyntaxSection(const char* line, int32 length,
 	int32& _column, BPoint& _offset)