Fix exception when converting to decimal values that reduce to N/1.

Before this the loop wouldn't terminate until the denominator had been
reduced to 0 and trying to create a GncRational with a 0 denominator
throws.

libgnucash/engine/gnc-numeric.cpp

@@ -368,7 +368,7 @@ GncNumeric::to_decimal(unsigned int max_places) const
         rr_num *= factor;
         rr_den *= factor;
     }
-    while (!rr_num.isZero() && rr_num % 10 == 0)
+    while (!rr_num.isZero() && rr_num > 9 && rr_den > 9 && rr_num % 10 == 0)
     {
         rr_num /= 10;
         rr_den /= 10;

libgnucash/engine/test/gtest-gnc-numeric.cpp

@@ -548,4 +548,16 @@ TEST(gnc_numeric_functions, test_conversion_to_decimal)
     EXPECT_NO_THROW(r = c.to_decimal());
     EXPECT_EQ(27434842, r.num());
     EXPECT_EQ(100, r.denom());
+    GncNumeric d(11900000000, 85000000);
+    EXPECT_NO_THROW(r = d.to_decimal());
+    EXPECT_EQ(140, r.num());
+    EXPECT_EQ(1, r.denom());
+    GncNumeric e(11050000000, 65000000);
+    EXPECT_NO_THROW(r = e.to_decimal());
+    EXPECT_EQ(170, r.num());
+    EXPECT_EQ(1, r.denom());
+    GncNumeric f(5000000000, 50000000 );
+    EXPECT_NO_THROW(r = f.to_decimal());
+    EXPECT_EQ(100, r.num());
+    EXPECT_EQ(1, r.denom());
 }