Issue #532631: Apply floatformat changes to unicodeobject.c

as well as stringobject.c.

Objects/unicodeobject.c

@@ -8286,6 +8286,15 @@ formatfloat(Py_UNICODE *buf,
         return -1;
     if (prec < 0)
         prec = 6;
+    /* make sure that the decimal representation of precision really does
+       need at most 10 digits: platforms with sizeof(int) == 8 exist! */
+    if (prec > 0x7fffffffL) {
+        PyErr_SetString(PyExc_OverflowError,
+                        "outrageously large precision "
+                        "for formatted float");
+        return -1;
+    }
+
     if (type == 'f' && fabs(x) >= 1e50)
         type = 'g';
     /* Worst case length calc to ensure no buffer overrun: