removing exception dep, saving blank canvas on checkRanges err

_examples/basic/main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"log"
 	"net/http"
 
 	"github.com/wcharczuk/go-chart"
@@ -38,5 +39,5 @@ func drawChartWide(res http.ResponseWriter, req *http.Request) {
 func main() {
 	http.HandleFunc("/", drawChart)
 	http.HandleFunc("/wide", drawChartWide)
-	http.ListenAndServe(":8080", nil)
+	log.Fatal(http.ListenAndServe(":8080", nil))
 }

chart.go

@@ -97,6 +97,8 @@ func (c Chart) Render(rp RendererProvider, w io.Writer) error {
 
 	err = c.checkRanges(xr, yr, yra)
 	if err != nil {
+		// (try to) dump the raw background to the stream.
+		r.Save(w)
 		return err
 	}
 

file_util.go

@@ -4,8 +4,6 @@ import (
 	"bufio"
 	"io"
 	"os"
-
-	exception "github.com/blendlabs/go-exception"
 )
 
 var (
@@ -26,7 +24,7 @@ func (fu fileUtil) ReadByLines(filePath string, handler func(line string)) error
 			handler(line)
 		}
 	} else {
-		return exception.Wrap(err)
+		return err
 	}
 	return nil
 }
@@ -46,7 +44,7 @@ func (fu fileUtil) ReadByChunks(filePath string, chunkSize int, handler func(lin
 			handler(readData)
 		}
 	} else {
-		return exception.Wrap(err)
+		return err
 	}
 	return nil
 }