StorageManager: remove unnecessary calculations on addr for next area

When writting or reading a block, if the block doesn't fit the area where it begins, the next base address is always zero. Thus the calculations to define the next value of addr are unnecessary.

Here's a quick validity proof using the previous calculations:
    First: Considering the case where the block doesn't fit it's first area:
        That means that (count + addr > length), what makes:
            count = length - addr; (1)
        So the following operations:
            addr += count;
            addr -= length;
        Are the same as doing:
            addr = addr + count - length; (2)
        Using (1) and (2) we have:
            addr = addr + length - addr - length = 0

    Second: When the block fits the area where it's at:
        That means that variable count is not changed,
        thus (n -= count) evaluates to 0, which makes the loop exit.

Another change was (b += count;) being moved after the condition to break the loop, since we just need to move the block pointer when it doesn't fit the first area.

libraries/StorageManager/StorageManager.cpp

@@ -150,15 +150,15 @@ bool StorageAccess::read_block(void *data, uint16_t addr, size_t n) const
         }
         hal.storage->read_block(b, addr+offset, count);
         n -= count;
-        addr += count;
-        b += count;
-
-        // adjust addr for next area
-        addr -= length;
 
         if (n == 0) {
             break;
         }
+
+        // move pointer after written bytes
+        b += count;
+        // continue writing at the beginning of next valid area
+        addr = 0;
     }
     return (n == 0);
 }
@@ -190,15 +190,15 @@ bool StorageAccess::write_block(uint16_t addr, const void *data, size_t n) const
         }
         hal.storage->write_block(addr+offset, b, count);
         n -= count;
-        addr += count;
-        b += count;
-
-        // adjust addr for next area
-        addr -= length;
 
         if (n == 0) {
             break;
         }
+
+        // move pointer after written bytes
+        b += count;
+        // continue writing at the beginning of next valid area
+        addr = 0;
     }
     return (n == 0);
 }