Don't hide line parsing errors

fixtures/invalid1.env

@@ -0,0 +1,2 @@
+INVALID LINE
+foo=bar

godotenv.go

@@ -149,11 +149,13 @@ func readFile(filename string) (envMap map[string]string, err error) {
 
 	for _, fullLine := range lines {
 		if !isIgnoredLine(fullLine) {
-			key, value, err := parseLine(fullLine)
+			var key, value string
+			key, value, err = parseLine(fullLine)
 
-			if err == nil {
-				envMap[key] = value
+			if err != nil {
+				return
 			}
+			envMap[key] = value
 		}
 	}
 	return

godotenv_test.go

@@ -278,3 +278,11 @@ func TestErrorReadDirectory(t *testing.T) {
 		t.Errorf("Expected error, got %v", envMap)
 	}
 }
+
+func TestErrorParsing(t *testing.T) {
+	envFileName := "fixtures/invalid1.env"
+	envMap, err := Read(envFileName)
+	if err == nil {
+		t.Errorf("Expected error, got %v", envMap)
+	}
+}