tests/float: Add test for parsing a float from an empty string.

tests/float/float1.py

@@ -22,6 +22,10 @@ print(float("infinity"))
 print(float("INFINITY"))
 print(float("nan"))
 print(float("NaN"))
+try:
+    float("")
+except ValueError:
+    print("ValueError")
 try:
     float("1e+")
 except ValueError: