[gjs] coverage: Add sanity check for rollback into negative lines

[Sam Spilsbury <samspilsbury src gnome org>]

commit 6e63501138d905d517df74d318cc1a322dfb4d11
Author: Sam Spilsbury <smspillaz gmail com>
Date:   Tue Jun 16 01:23:34 2015 +0800

    coverage: Add sanity check for rollback into negative lines

 modules/coverage.js |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/modules/coverage.js b/modules/coverage.js
index ec94adb..9255540 100644
--- a/modules/coverage.js
+++ b/modules/coverage.js
@@ -529,7 +529,7 @@ function _incrementFunctionCounters(functionCounters,
             --line;
             functionKey = name + ':' + line + ':' + nArgs;
             functionCountersForKey = functionCounters[functionKey];
-        } while (linesWithKnownFunctions[line] !== true);
+        } while (linesWithKnownFunctions[line] !== true && line > 0);
     }
 
     if (functionCountersForKey !== undefined) {